While not a quandary to keep the population awake at night, creating and perfecting the track-focussed sports car is far from the work of a moment. The same issue faces this pair, the McLaren 600LT Spider and AMG GT R Pro, as it does the 911 GT3 RS, Huracan Performante, 488 Pista and so on. Chiefly it's one of compromise, especially when the base cars - the McLaren 570S and AMG GT S, in this case - are already so good. Because if the 'ring warrior is made too hardcore, if all its usability is sacrificed at the altar of apex speed, it'll be of no use on the road to the racetrack. When spending £200,000 on what will likely be a circuit toy, why not go the whole hog and buy the race car?
On the other hand, if the overhaul is too modest, if it feels a half-baked and cynical cash in on motorsport kudos, then the lairy paint job and big exhausts struggle to justify the premium over the standard model. If little is gained dynamically, but a buyer is forced to endure all the compromise of something stripped out, then what's the point? As mentioned, those standard cars aren't exactly shambolic on track anyway.
It's a tiny little niche that these two are operating in, then, with precious little margin for error. The last thing anyone wants in a cold, wet, windy Wales is a spiky sports car, one optimised only for two hot Wednesdays in August. And nobody wants to travel that far to find a car that feels like standard, just more expensive, louder, and with stripes.
There seems little danger of that happening with the McLaren 600LT. It's a car that's well known now, its seamless melding of devastating pace with angelic tactility and supercar drama as compelling a recipe as you'll likely find. There's an argument to say it's a little familiar, its tricks similar to those pulled out of the 675LT's hat of being damn near as civil and as silly as you'll ever need, but that seems like criticising AJ for one more crushing knockout - sure, it's an experience a lot like before, but no less awe-inspiring to witness.
The Mercedes is a far less familiar quantity. Derived from the belligerent GT R, a car we've only tried on track, the Pro ramps the anger up yet further with modifications that scream 'RACE CAR!' like an overexcited toddler: manually adjustable coilovers - on a Mercedes-Benz - with tinkering possible on spring pre-load, rebound, low-speed and high-speed compression; fully rose-jointed rear wishbones, where it was only lower wishbones on the GT R; a further-stiffened chassis thanks to a carbon shear panel, with retuned engine and transmission mounts to compensate; forged wheels, ceramic brakes and yet more aero fettling. So much so, in fact, that there's 100kg more downforce than a GT R at 155mph, with two-thirds of it over the front axle. As you might have seen, it's all sufficient for a ludicrous 7:04 lap time at the Nordschleife.
But therein lies the (quite considerable) problem: what if the Pro is just, well, a bit too Pro? What if it's too stiff, low, loud and silly for everyday use? Then we're back exactly where we started, with a car that doesn't occupy either niche of sports car or track car with any conviction - remember this is only as powerful than the GT R, and actually 20kg heavier.
The Pro is no less intimidating to bimble around in, either, it possessing that same hot-rod driving position - where you sit a long way back, the enormous plain of a bonnet swelling out front - as any other GT. Visibility is hindered further by the standard-fit cage and what feel like lower (but much better) seats, the vicious crabbing at manoeuvring speed and the prodigious width only fraying nerves further. Especially so, as every single person nearby is looking at the rude Mercedes with the pugnacious stance, day-glo stripe and evil V8 war cry.
Pleasingly, though, the Pro is nowhere near as obstinate as it might first seem. Sure, the dash is busy (and the gearstick almost in the boot), but it feels lavishly appointed, opulent and inviting in a way that no other road racer ever does. The materials are rich, the graphics vivid and the stereo immense; while we all care about purity of experience and crispness of response, most people don't live near racetracks - and a five-hour drive is genuinely one to be embraced in the Pro.
Because beyond all the trinkets and niceties, this thing drives, too. Not simply in a ground covering, does-the-numbers fashion, but in the sort of engrossing, absorbing way that makes you marvel at its ability, test its reserves and lap up every single second of the experience. Because there's not much that's this good.
Even before Wales, the AMG isn't a long way off bewitching. The new suspension is a revelation, delivering purposeful, taut, absolute control, yet never entirely at the expense of comfort. It's pretty burly around town, yeah, but only in the same way a C63 might be. At speed there's precision and seemingly infinite, delicate finesse, far beyond a standard GT and with a distinct motorsport vibe. It's still wider than is comfortable sometimes - a point forcibly made by the thump of cats eyes on the A5 - but the new-found dynamic assurance and sheer intensity of the experience are undeniable.
Combine that poise with the monstrous powertrain, heroic brakes and sheer theatre of such a naughty V8 Mercedes and the GT R Pro has made a friend by Snowdonia. Because it's absolutely awesome, defying the bruising aesthetic with some real subtlety and depth.
But can it actually be as awesome as a Longtail McLaren? The 600LT is a car that, after all, is frequently cited as the best thing to leave Woking in its eight years of making supercars, one that sold out almost as soon as it was announced and that has been sweeping aside the established supercars ever since. Even on a morning as dark and monochrome as the car's Chicane Grey paint, nothing will ever dim the excitement of a Longtail drive. Because you just know it'll be good.
Look at the spec, for starters. Even as a Spider to the AMG's coupe body, this is 170kg lighter, more powerful and therefore even quicker. A coupe shaves another 40kg again. We all know about McLaren's famed work with suspension and steering for the UK, the accolades the cars have accrued and the fawning, ceaseless praise that's contributed to the reputation.
The LT doesn't disappoint. Daft thought it will sound for a 600hp, mid-engined car, the McLaren is welcoming, accommodating and simple where the AMG was thuggish, threatening and imposing; you can see out, steer it with greater confidence, feel integral to what's going on straight away and glide over imperfections that the Pro would rather scrap with. For cars with such similar remits the initial impressions are markedly different.
From there the LT continues to impress, deft and supple yet with a backing choir of titanic performance and expertly-honed dynamic focus. It's arguably more faithful and trustworthy in the first few miles than the Pro ever is, the fabled hydraulic steering really brought to the fore; the response more natural and the feedback more authentic than the AMG's variable ratio, four-wheel steer system. The 600's agility is bestowed by its genuinely low mass, meaning the confidence in it is abundant because there's something tangible to work against, as opposed to fancy tech that needs considerable faith placing in it.
Moreover, because of the weight saving over a regular (very good) Sports Series, the LT reaps a whole host of rewards that the Mercedes won't over its siblings. The savagery of the performance is greater, the immediacy heightened, the ability to engage and entertain raised to a point it's never been. The 570S already scores highly on these fronts, but the 600 redoubles the effort: the ignition cuts puncture the air viciously (and hilariously) with every upchange, the Senna seats clamp you into every bit of the action, the uprated brakes (also Senna-derived) mightily powerful and ideally weighted, if slightly dead at the top. It's all the lovely, granular ingredients of a lightweight sports car, right down to roofless motoring if you so wish, only with 200mph potential sprinkled on top. Then flambéed by those incredible exhausts.
Surely, however good it might be, the Mercedes can't match the vividness of that experience? Gah, it's a tricky one, because there are evidently things this AMG does better than that LT. The powertrain is joyous, the V8 more responsive and satisfying than the McLaren's, better to listen to and with a dual-clutch 'box that's at least its equal. And it has better shift lights. The assists are actually better calibrated, too, the interventions of the Pro if anything less invasive than in the McLaren. Which was already fantastic.
Furthermore, because the involvement of the GT R gradually increases trust, you can experiment with that incredible traction control to your heart's content. What's initially the scariest AMG sports car slowly becomes the most welcoming and the most rewarding - the best AMG sports car, put simply - one click at a time. Because of where that V8 is, there's mid-engined agility but front-engined balance, enormous traction but something fairly benign behind it, a greater sense of connection through hands and bum than any other GT and a realisation, slowly but surely enough, that it won't kill you. But it was nice to be a bit scared. The McLaren in some instances can feel spikier, the lag and open differential occasionally making it, if not clumsy, then not the precision instrument it always otherwise feels.
How to sum them up succinctly? The McLaren is immediately the more rewarding and absorbing driver's car, delivering everything brilliant we've come to expect from Longtails in recent history. We know from track driving, too, that its road manners are not at the expense of circuit thrills. It's a consummate lesson in chassis engineering and the better car to drive: confidence inspiring, flattering, cohesive, freakishly competent and wholly intoxicating.
But it's not the winner. Because while the GT R Pro is not the McLaren's equal in finger-tippy interaction - nothing is - it's extremely close, and it surpasses the Woking wonder elsewhere. That it's initially such a terrifying car, one that gradually reveals itself to be something far friendlier and adept, means the Pro is a car you just want to keep driving, keep pushing, keep discovering. The McLaren, great though it is, offers up its genius far more freely, and soon feels to be more of the same - the Mercedes is unlike anything else from Affalterbach. The AMG's steering isn't the equal of the LT's, sure, though with time comes trust in its prodigious talent, and there's more confidence here than in a typically aloof standard GT.
Then, on the way home, when the McLaren is buzzing and fizzing along the motorway, infotainment screen sluggish and seat uncomfortable, the AMG only seems more desirable. Some have criticised its luxury, suggesting that it compromises the Pro's track integrity; on the contrary, it gives the car incredible duality, damn near as exciting as the McLaren yet considerably more liveable as well. That compromise mentioned right at the beginning feels more comprehensively delivered by the AMG, suiting as it does everything thrown at it, than the LT - inspirational in the right situations, infuriating in others.
Offered one for 15 minutes again in Wales, the McLaren is still the best, and arguably unmatched as a visceral, exhilarating, intense road car experience. Offered one for a year, though, the Pro would win; brimming as it is with attitude, intrigue, vats of talent and heaps of brutish charm to learn about and admire. It's an absolute triumph from AMG, a realisation at last of the GT's latent talents and a handy £70,000 less than the McLaren as tested here. Bring on that track test - the big, bad, brooding Mercedes is more than ready.
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)
Weight: 1,406kg (DIN kerbweight, without driver)
CO2: 276g/km (WLTP)
Price: £201,500 (price as tested £258,440, comprised of Chicane Grey Elite Paint for £3,660, Gloss Visual Carbon Fibre Exterior Upgrade Pack 2 (Front Splitter with Integrated Twin Endplates, Side Skirts with Aero Winglets, Rear Bumper with Integrated Full-Width Diffuser, Rear Bumper Aero Fins and Rear Spoiler) for £5,870, MSO Defined Gloss Carbon Fibre Exterior Upgrade Pack 3 (Fixed Rear Wing, Exterior Door Inserts, Rear Deck, tonneau Cover and Service Cover) for £17,650, MSO Defined Gloss Carbon Fibre Front Fender Louvres for £9,960, Carbon Fibre Interior Upgrade (Interior Components, Interior Door Inserts and Tunnel Sides) for £5,670, Power Adjust Steering Column with Comfort Entry/Exit for £1,420, By McLaren Alcantara LT Interior for £3,080, Soft Close Doors for £640, 12-speaker B&W Audio System for £3,640, Security Pack for £3,980, McLaren Track Telemetry with Lap Time Function and Three Cameras for £1,370)
SPECFICIATION - MERCEDES-AMG GT R PRO
Engine: 3,982cc V8, turbocharged
Transmission: 7-speed dual-clutch automatic, rear-wheel drive
Power (hp): 585@6,250rpm
Torque (lb ft): 516@1,900-5,500rpm
0-62mph: 3.6sec (claimed)
Top speed: 198mph (claimed)
Weight: 1,575kg (DIN, without driver)
Price: £188,425 (and £188,425 as tested!)
Images: Sim Mainey