The Spider, launched only a few months ago, merely seals the deal. For a weight penalty equivalent to two large suitcases, the car will have its composite roof panels slung in the back within 15 seconds - and thanks to the carbon fibre tub underneath, requires no sacrifice of the 570S's torsional rigidity to do so, meaning that all the same handling superlatives still apply. Which is a vanishingly rare fact, even in this segment. Take it from us, on a scale of righteous combinations, the Spider is right up there with hops and water.
So what chance the new Audi R8 Spyder Plus? Well, being the latest, greatest and most powerful version of the convertible yet does it no harm, nor does that fact that its with-options price is some £50k cheaper than the McLaren. Ingolstadt's supercar cedes no ground to any rival in the brand allure stakes either. I'm still not convinced the current generation of R8 is quite as timeless as the original (or as delicately pretty as the McLaren) but it definitely commands attention. Lose the super-light cloth hood behind the revised bulkhead and its chiseled lines resurface, bolstered by a rear deck that hunches high over your shoulders and has the Spyder bristling with thickset charisma - even if it arguably needs a shade of paint lighter than the Monterey Green featured on our test car.
Move between the two though and you'll need to be dead inside not to feel slightly deflated by the R8's refusal to have its driver door swing upwards past your sunglasses. Call them a faddish piece of engineering whimsy if you like, but dihedral doors are rather like having Nick Cave or Jason Leonard or one of the Coen brothers as a godfather; no, it isn't strictly necessary - but it's a damn sight cooler with than without. Of course, on the inside, the Spyder owner does without nothing. At night - when I meet the R8 on route to Wales - the first stab of the wheel-mounted start button rouses a small mountain of LEDs and dinky spot lights, capped by the i-Cockpit's super-slick (if occasionally perplexing) instrument cluster.
Bathing in its phosphorescent glow ought to be satisfying for anyone who spent their formative years sleeping six feet from a Playstation - but it pales in comparison to the warmth and fuzziness associated with the second stab of the button, which raises the theatre curtain on the main event. The naturally-aspirated 5.2-litre V10 is permitted the briefest whir of starter, then Audi has it growling at you like a grumpy tiger. The noise - familiar, rich-edged and deliciously lean - ought really to encompass leather on willow too, for it is also the sound of the McLaren's rapacious 3.8-litre V8 being tonally knocked for six. And we haven't even moved yet.
To do so obliges you to nudge the airliner-style gear lever into Drive, and then marvel at how effortlessly the R8 slips its mooring. It's like runny honey at slow speeds; the seamless interaction of engine and gearbox making the normally amenable (yet heavy-pedaled) McLaren seem ostentatious in comparison. It's precisely the kind of user-friendliness which has you immediately driving the Spyder guiltlessly fast and without the strained attention typically demanded by a supercar.
Certainly on the M4, the R8 snaps into a dead-eye fast lane posture that speaks to endless development miles spent at ludicrous-speed on the Autobahn. In the 570S, clamped into the optional race seat, you steer with both hands and change lanes like you're warming the tyres at Monza. In the Audi you feel your mindset recline; let the fine Nappa leather soak you up, and fiddle incessantly with the multi-layered infotainment. One moderately surprising thing you don't do is miss the twin blowers mated to Ricardo's flat-plane V8; so much better is Audi's seven-speed dual-clutch 'box at automatically downshifting in its default mode than McLaren's SSG transmission. Combine that with a much crisper throttle response and the warbling soundtrack, and the R8's persuasiveness lengthens.
It is also, for as long as the motorway lasts, in the same ball park as the 570S's superlative levels of ride comfort. Not in the same tier perhaps, and certainly not the same row, but - equipped with the (scandalously cost-option) Magnetic Ride dampers and kept in Comfort - it is easily supple enough for England to turn agreeably into Wales, with only a marginal quiver of the scuttle to show for the structural decapitation of its space frame. Sure, the longitudinal body movements aren't quite as unencumbered as in the McLaren, but you'd have to drive them back-to-back to notice - or care.
Compared to the R8's snugly upholstered cabin, the 570S is like a petrified park bench. Practically every surface you come into contact with is beautifully trimmed - but also unapologetically solid. True, this is partly to do with the aforementioned race seats, although the steering wheel and dashboard are similarly brusque to the touch; the suede veneer pulled so taut it's like skin over shin bone. This makes the car acutely tactile to sit in, and via its enormous paddle shifters, intransigent infotainment screen and a brace of machined metal pedals, very substantial to interact with.
If the downside of this approach is a mild impairment of the car's jump-in-and-go ease of use, the upside is almost unbroken tunnel vision from its driver. Much like a Caterham 7 or a Lotus Elise, the 570S wants your undivided attention, and with it assigned - and the M4 swapped for a Welsh B road at dawn - it starts to do extraordinary things. Or at least it does once you've lit the Active Dynamics Panel on the centre console and rescued the powertrain from its slightly anemic (i.e. fuel-saving) Normal mode. With Sport selected, the V8's response sweetens considerably and has you indulging the paddles almost immediately.
The net result, rather inevitably, is a grander, gruffer level of performance. Attempting to separate it from the R8 purely on the grounds of straight-line, through-gear speed though is a bit like choosing between Margot Robbie and Gal Gadot based on the evidence of a GQ shoot. They're both otherworldly. They're both too good for you. The 570S has 570hp at 7,500rpm; the Audi, 610hp at 8,250rpm. They hit 62mph in 3.2 and 3.3 seconds respectively. They are monsters on road, and for the most part - especially from a standing start - they're explosive to the extent where they might be considered equal.
Like the R8, the baritone McLaren is best enjoyed at beyond 7000rpm - but, as with the Audi, getting there in any ratio beyond second potentially means putting yourself at the mercy of an extremely grumpy magistrate. A sense of self preservation tends to keep you between 3,000-6,000rpm in latter gears, and in this region, the Brit's stupefying capacity for surging forward like a ball bearing from a slingshot is not matched by the spine-tingling German.
Clearly a longer wait for a moderately lower peak torque figure has something to do with this - the V10 not supplying its 413lb ft until 6,500rpm compared to the V8's 443lb ft at 5000rpm (with 80 per cent of it on tap from 2,000rpm) - but there's also a prominent difference in kerbweight to take into account. Dry, the R8 weighs 1587kg; 228kg more than McLaren's claim for the Spider. With fluids that shortens to 209kg, but it's still enough for a 54lb ft deficit in torque-to-weight; a figure easily large enough to have real-world consequences.
Certainly in Wales, there is no need for fag-packet mathematics - the Audi feels more onerous on its double wishbones, and the notion is frequently in play when pushing on. Some of this heft is cleverly parlayed into Ingolstadt's preferred dynamic quality: namely the confidence inspiring and road smothering traction summoned up by the all-wheel drive system. It is to the engineers' credit that this sense of accuracy doesn't overwhelm the R8's mid-engined identity, nor blunt the flat-bodied fierceness of its change of direction - but, to a greater extent than in the previous model, there is no mistaking the Spyder's bullnecked belligerence in moments where its rival ebbs and flows.
Undoubtedly the McLaren highlights some of the underbody toil occurring. The roads spiraling away from the Afan Forest Park throw up the traditional combination of lateral stress and surfacing eccentricity, and for the first time the idea of the R8 being more susceptible to flex comes significantly into play. Broadly speaking, the modifications made to the Audi's aluminum spaceframe in the name of stiffness are entirely laudable - but there is no doubt that compared to the carbon-tubbed 570S it feels braced from the underside, and under duress some vibrations quiver upwards, looking for a roof which is no longer there.
The McLaren tolerates no such intrusion. Its wheel control at speed is uncanny: obstacles that would trouble the far more liberal spring travel of a well-sorted hot hatch are swept into a thresher also made of double wishbones and adaptive dampers, and returned to the driver as a poised, précised reading of the road. Its relative comfort (even in the firmer Sport mode) is less a feature though than the sense of assurance it radiates. Because it is rarely ever upset, it seems eminently in control of an increasingly precarious situation without sacrificing any of its deftness for a greater stability bias. It is in control of the road - and you are in unequivocal control of it.
The steering doesn't even seem especially reactive after the less sensitive Audi - it just turns progressively, profoundly and without a shred of the hazy, synthesized resistance that tends to inflict even the finest electrically-powered systems. As an old-fashioned conduit between you, the front wheels and the road, it is sensational; less because you marvel at the car's unwavering response to your inputs, and more because your input itself is based on the unending communiqué coming in the opposite direction.
The result is straightforward: while you start at one end of a wet road expecting the R8's driven front axle to lend you all the confidence in Christendom, it's actually the rear-drive Spider which emboldens you to take all manner of liberties with its forgiving talent. And while that has much to do with the understeer-thwarting adhesiveness of its front end (and the R8's tendency to slightly overindulge its nose with power), it is also a direct consequence of being so explicitly informed about the car's limits - be it through the steering or the super-rigid seats.
Ultimately all of this serves to point out the pleasure of driving the McLaren rather than necessarily thwarting the appeal of the Spyder. After two full days the 570S is magnanimous in victory; the R8 still splendid in defeat. In retrospect, both are best characterized by the drive mode they excel in. No matter how comfortable and consistently usable the 570S's 'normal' setting might be, the extraordinary serrated edge yielded by placing the powertrain in 'Track' and the chassis in 'Sport' has you indulging the active panel at practically every given opportunity.
In the R8, it is the 'Comfort' mode that best obliges your sense of enjoyment: the most relaxed damper setting and steering attitude not dulling down the car's remarkable traction or its dazzling powerplant one bit. The rub, of course, is that the 570S can do contented, amenable progress better than the Audi can do the feelsome, flat-out stuff - a fundamental talent imbalance that ensures McLaren bragging rights virtually from the get go. However, it doesn't negate the R8's unrivalled ability to go from leisurely open-top to snarling supercar in about 40mm of accelerator travel; a knack the 570S doesn't possess with anything like the same pleasure payload.
This makes the Spyder likeably different from the Spider - and clearly that's a good thing, because the direct comparison does serve to confirm that Woking's standard-bearer is among the best cars on sale today for any price. The R8 remains a formidable prospect, one that conscientiously balances both ends of the spectrum: managing to be spectacularly usable, luxurious and accommodating whilst simultaneously finding itself endowed with one of this century's truly compelling atmospheric engines and a chassis to oblige it. Less complete than the lighter, pricier 570S it may very well be, but simply providing access to both - and the blue sky above - guarantees the model's relative greatness.
AUDI R8 SPYDER V10 PLUS
Engine: 5,204cc, V10
Transmission: 7-speed S-tronic automatic, all-wheel drive
Power (hp): 610@8,250rpm
Torque (lb ft): 413@6,500rpm
Top speed: 204mph
Weight: 1,770kg (EU including 75kg driver)
MPG: 22.6 (NEDC combined)
Price: £144,335 (As tested £172,745 comprising £3,400 for Monterey green, £7,000 R8 sports seats in Audi exclusive Cognac brown fine nappa leather with diamond stitching, £1,350 for 20-inch 10-spoke Y design forged aluminium wheels with a diamond cut finish, £600 for parking system plus with reversing camera, £3,000 for LED headlights with Audi laser light and high-beam assist, £250 for Audi smartphone interface, £450 for Audi phonebox with wireless charging, £1,800 for Sport exhaust system, £1,600 for Audi magnetic ride, £275 for cruise control, £475 for pneumatic seat backrest and side bolster adjustment, £450 for fine nappa leather upholstery and trim, £2,750 for extended fine nappa leather package, £600 for Audi exclusive door sill trims with illuminated sill plates, £750 for audi exclusive leather controls, £325 for Audi exclusive floor mats, £650 for constrast stitching for extended fina nappa leather package and £2,685 for on the road costs)
MCLAREN 570S SPIDER
Engine: 3,799cc, twin-turbo V8
Transmission: 7-speed SSG automatic, rear-wheel drive
Power (hp): 570@7,500rpm
Torque (lb ft): 443@5,000-6,500rpm
Top speed: 204mph
Weight: 1,486kg (DIN, inc. 90 per cent fuel)
MPG: 26.6 (NEDC combined)
Price: £164,750 (As tested £226,710 comprising £1,440 for Curacao blue special paint, £2,690 for 10-spoke lightweight forged alloy wheels, £910 for McLaren orange coloured brake calipers, £3,370 for sports exhaust, £2,570 for By McLaren designer interior sport design 3 with carbon black alcantara and stone grey nappa leather, £5,110 for Carbon fibre race seats, £1,870 for Carbon fibre sill finishers, £2,070 for vehicle lift, £1,000 for front and rear parking sensors, £2,150 for McLaren track telemetry, £640 for vehicle tracking system, £3,240 for carbon fibre exterior pack 1 in gloss black including door mirror casings and side air intakes, £8,770 for Carbon fibre exterior pack 2 in gloss black for aero blades, side skirts and diffuser, £5,510 for Carbon fibre interior pack including switch pack surrounds, steering wheel spokes, gearshift paddles, interior door inserts and tunnel sides, £5,740 for MSO defined carbon fibre rear deck and tonneau cover, £6,320 for MSO defined Carbon fibre exterior door inserts, £4,280 for MSO defined Carbon fibre front splitter and £4,280 for MSO defined Carbon fibre rear bumper)