Without sharing a shred of commonality in the way they're put together, the McLaren 600LT Spider and Porsche 911 Turbo S Cabriolet embody open-top motoring at its finest. One is mid-engined, highbrow talent honed to a bewildering point. The other is just bewildering. But both make prodigious use of boost to achieve output in the +600hp range, both have a sub-three-second 0-62mph time and a top speed which surpasses 200mph. Both open to the elements. Both make a summer's day special. They slice the cake in different ways, but both want you to have it and eat it. Price disparity aside, they are hard to separate on paper.
To drive, each sets its stall out early. Motorway miles in the Turbo S dissolve like sugar in stirred water. Clearly there is the latent performance, so prodigious in gear that you feel like an F1 car held on a yellow flag - but there is also a level of directional stability which seems astonishing even for an all-wheel-drive 911. You'll have heard about the Turbo S's slightly fidgety secondary ride, and there's no use denying it in the Cabriolet, yet at sustained speeds it's supplanted by a rubbery suppleness that deals with low frequency undulations effortlessly.
The pay-off is a 911 Turbo speciality: you sink into the ultra-low, dependably snug driver's seat and then miraculously turn up wherever you were headed ahead of time and completely unruffled. You will forget that the material above you is spun from fabric. It's entirely possible to hold a quiet conversation while travelling at high speed, even in a car sat 10mm lower on optional PASM Sport Suspension and rolling on 20/21-inch Exclusive Design wheels. It's entirely possible to lose your license in a thoughtless moment, too, so supremely tractable is the twin-turbocharged 3.7-litre flat-six. Had we shot this job in Ullapool there would have been no complaint from the 911's guardian. It is effortlessly good over distance.
The 600LT is harder work. Not because it's less cleverly sprung (McLaren's miraculous ride quality shows up the 911 around town) but because it implies a subtle level of stress that the Porsche strives to alleviate. Part of this, naturally, is about fitness for purpose. The LT is intended to be scalpel-sharp and hyper responsive and therefore sacrifices some ease-of-use aspects by default. But it doesn't turn its clever hard top or smaller wheels into a cruising advantage either, and nor does it encourage you to watch the world go by. There is cruise control. But no autopilot.
Its interior, filleted for lower weight, makes fewer concessions, too. Take away the oblong touchscreen and digital instrumentation panel and you'd not be so far from Woking's GT4 package. It's colder and airier and less opulently trimmed than the 911. Its leanness is typified by the super lightweight carbon fibre race seats (a £5,140 option), which grip you like a proper motorsport bucket. Second to their closeness is the proximity of each axle: the 600LT feels compact like no 992 ever could. The arches barely seem forward of your toes; your passenger more bedfellow than casual acquaintance.
The Turbo S doesn't want to be pocket-sized, though - it wants to be plush. Expect the raised centre console to meet your left elbow and the door card to bolster your right. No human would countenance the back seats, but rucksacks and hand bags are easily accommodated. Practically speaking, the Porsche is in a different league; technologically, it's on another planet. Push a button that isn't connected to anything mechanical, and the 911 romps clear of its rival. If McLaren dedicated itself solidly and solitarily to the business of making an infotainment system, it might compete with Stuttgart's digital armoury by the end of the decade. Right now it is like comparing a Sony Playstation to fish.
In a perfect world, Porsche would like that difference to be manifest in every other aspect of the Turbo S's use. This is why its flat-six starts up with a flutter and settles into a silk-smooth tick over. Even with the roof down, the motor is agreeably quiet. Its maker could have it bleat and quiver like a transformer if it wished it; but that is not the point of the topmost 911. It's about walking softly while in possession of a howitzer. The 600LT meanwhile, won't let you enter a sat nav destination without engendering despair - but it counters this with sound and fury from its upturned exhaust nozzles. A child would waste no time pondering the 911's tailpipes. Yet they will stare at McLaren's valves endlessly; longer if their hands need warming. Adults, too.
For Porsche the drama is less about theatrics. It wants to be about function. And everything you've heard about the Turbo S's function is true. Thanks to its extraordinary engine and impeccable PDK transmission, it goes from staid to supernova at anything over half throttle. It wants to sooth your furrowed brow and then rearrange your internal organs: that is the venerated Turbo S way. Forget 590lb ft of torque from 2,500rpm. Think time travel. But then think of it not as a threatening, seat-of-the-pants thing, but rather as something approachable and easily quantifiable; like an afternoon stroll conducted at warp speed.
If you think you'd probably be a little conflicted about that prospect, you're not wrong. On the one hand, it's scarcely believable. Were it not so prodigiously fast in a straight line, the 992's dynamic tranquility might be its undoing. But the car delivers such monumental in-gear performance that no one with working faculties could fail to notice that they were strapped to something pretty special. Its neutrality, mobility and mechanical grip are astounding. Four-wheel steering and torque vectoring wizardry confer otherworldly handling gifts and only very occasionally does the 1,710kg convertible seem unfairly weighed down or short of an answer to a random bump or crest. It carries what extraneous mass there is low, but doesn't let it confer clumsiness. It is acutely unflappable.
On the other hand there is the 600LT; a tuning fork to Porsche's multi-faceted grand piano. Where the 911 depends on its explosiveness to help underwrite the experience, the McLaren's own immense straight-line speed plays second fiddle to an expressive chassis. As you might expect, this is partly about the benefit conferred by a mid-engine configuration, rear-drive and lower mass, but it's also about the level of feedback channeling up through the steering wheel and stiffer frame.
No-one tunes electric power steering with greater finesse than Porsche, but the merits of persisting with a hydraulic system are plain enough. The 600LT's rack is five per cent quicker than the one fitted to the 570S, however that doesn't make it overly reactive away from the straight ahead, it just crisply attains heft as lateral load increases on the chassis. Not only does this provide an elemental reading of the road, it also leaves you in no doubt about the adhesive limits of the Trofeo Rs stationed at each corner.
Consequently, while you might ultimately not carry any additional speed through a bend, you drive the McLaren round one not in a baffled state of unconcern, as you do in the Turbo S, but rather in nodding appreciation of what's actually happening. It probably helps that the 600LT gets a simplified chassis compared to more senior models, aiding its consistency and adding to the impression that the car needs none of the Porsche's computational finesse (though of course it has no shortage of it) to assure you that you're in complete control, and have a pivotal part to play in the car's performance.
That doesn't necessarily mean that you should expect additional throttle adjustability from the back axle - the LT's stickier tyres have a near unbreakable bond with public highway tarmac - although the McLaren will lift an inside front wheel if you really attack a bend, like a race car over an apex kerb. String a few corners together and inevitably it makes for a more visceral drive, ably soundtracked by the snap-crackle from the exhaust which accompanies every downshift.
Of course, you'll be executing plenty of those. The V8 is noticeably laggier than the flat-six under 3,000rpm, and it does not have a seamless gearbox to fall back on. McLaren (with third-party help) built its twin-turbocharged unit to work best at 8,000rpm and you're forced to work with that defining trait, rather than revel in a seemingly infinite supply of performance, as you can in the Porsche.
Should you not wish to stray so far from that mighty stockpile, we'd understand. Rendering a preposterous output usable is the Turbo S's calling card, and no previous generation of the model has granted quite so much accessibility to such a large number. Moreover, it's possible that there is no other car on sale today quite as impassive or confidence-inspiring in fast corners. And it is so eerily well sorted that it makes every corner a fast one.
But as a car - and more specifically as a supercar doing supercar-type things - it remains in the shadow of the McLaren 600LT. It is very likely that you might drive the 911 quicker everywhere (in the rain, you definitely would) but you would not relish the experience in the same way. Probably the Spider doesn't make its significant weight advantage as telling as it might have otherwise been - so able and fast is the 911 - but really it's about the sense of inclusivity conveyed by its structural and control surface superiority. When you really want it to, when the road and conditions are perfect, the 600LT will make your head spin. It's about euphoria.
Obviously that does not confer perfection across the board. The Spider is intended to feel like a rapier, and does. It does not convincingly challenge the more affordable 911 in broader use, even allowing for the fact that it is more forgiving at slower speeds and does not let a solitary creak issue from its interior. If, for you, open-top motoring and more than 600hp simply must come with the underlying ability to drive anonymously to the shops or absorb hundreds of miles of motorway then the Turbo S has a bandwidth like nothing else. But it is only brilliant up to a point. To go beyond what it can do, you'll still need a McLaren.
SPECIFICATION | PORSCHE 911 TURBO S CABRIOLET (992)
Engine: 3,745cc, twin-turbocharged, flat-six
Transmission: 8-speed dual-clutch auto, all-wheel drive
Power (hp): 650@6,750rpm
Torque (lb ft): 590@2,500rpm-4,000rpm
Top speed: 205mph
Price: £165,127 (as standard; price as tested: £178,414, including £590 contrasting seat centres, £1,052 PASM Sport Suspension, £2,180 sports exhaust system, £1,608 20/21-inch Exclusive Design wheels, £434 black matrix LED headlights with Porsche Dynamic Light System, £732 Park Assist with Surround View, £749 Lane Keep Assist with speed limit indicator, £1,203 adaptive cruise control, £203 ioniser, £354 ambient lights, £1,313 air vents trimmed in leather, £161 model logo on centre console lid, £161 Porsche crest on front headrests, £291 leather sun visors, £2,256 Burmester high-end surround sound system).
SPECIFICATION | MCLAREN 600LT SPIDER
Engine: 3,799cc, twin-turbo V8
Transmission: 7-speed dual-clutch auto (SSG), rear-wheel drive
Power (hp): 600@7,500rpm
Torque (lb ft): 457@5,500-6,500rpm
Top speed: 201mph (196mph roof down
CO2: 276g/km (WLTP)
Price: £201,500 (as standard; price as tested: £249,840, including £3,660 Vermillion Red paint, £3,340 visual carbon fibre exterior pack 1, £5,870 visual carbon fibre exterior pack 2, £12,400 MSO Defined gloss carbon fibre exterior pack 3, £1,600 diamond cut wheel finish, £940 red brake calipers, £5,140 super lightweight carbon fibre racing seats, £2,630 carbon fibre interior components, £1,420 power adjust steering column with comfort entry/exit, £3,080 leather LT interior, £640 soft close doors, £3,640 12-speaker Bowers and Wilkins audio system, £3,980 security pack including nose lift).