Almost a decade and a half ago, at the Paris motor show of 2004, Mercedes revealed something nobody had seen before: the CLS55 AMG. Here was a four-door, four-seat executive car with the same powertrain as an E55 AMG, yet which cost more on account of its swoopy good looks and coupe glamour. It'll never catch on, came the cries; how wrong they were.
Today there are not only competitors from a host of different manufacturers, proving the validity - at least in terms of commercial success - of the flagship four-door coupe, but Mercedes' contemporary take on the idea is rather more serious again. The supercharger is long gone, of course, this new GT 4-door using the imperious twin-turbo 4.0-litre, yet power is up by 170hp and torque by 148lb ft. That old CLS was hardly lacking in potency, either, with 469hp and 516lb ft - be in no doubt, this GT is obscenely brisk, those colossal outputs only losing their battle with 2,000kg at 196mph.
Still, today is not for Autobahn antics, Drift Mode displays of singed Cup 2s or supercar-baiting lap times; along with the A35, the GT 63 has been launched over here in a freezing, wintry Scotland. It really doesn't get much more 'real world'. Not only does it mean the car is on Michelin winter tyres (the Cup 2 option is one of the things that marks a GT out from the E63), it means the various shenanigans possible through AMG Dynamics appeal as much as a swim in the nearby North Sea - too much danger of being exposed, doing yourself harm and achieving public notoriety. It'll be a sensible-ish drive at sensible-ish speeds, to establish whether the GT can justify its premium over the already mighty E63, and also to figure out its standing against rivals like the Porsche Panamera Turbo.
Is it fair for journalists in sweatshirts and trainers to comment on what a car costing £140,000 looks like? Probably not - yet here we are. It would be a stretch to call the GT 4-Door conventionally beautiful, though that's an accusation that could be levelled many a car nowadays. What the car definitely possesses is presence, a dramatic shape for this sector and some lovely details that make it look expensive even to those who know little about cars.
The interior is far easier to heap near-unequivocal praise on. By combining the switchgear arrangement seen in the two-door AMG GT and the sense of opulence found in the big Mercedes saloons, with new tech (like the wheel-mounted mode selector), the 63's interior is fabulous. It isn't too flashy, it isn't too restrained, it simply treads the line perfectly for a dynamic yet luxurious grand tourer.
By and large, that impression of impeccably struck compromise extends to the way the GT 4-door drives. While based on the MRA architecture that also underpins the E-Class, this GT has a stronger chassis than any stablemate and also receives a bespoke steering and suspension tune, presumably to make it feel a little more GT than 63.
In all honesty, with the caveat of having driven the two so far apart, the GT feels to ride very similarly at low speed to an E63. That means pretty rigidly in fact, car clenched and unrelenting even in the most accommodating setting of the AMG Ride Control+ suspension. Is it more excusable in a car of a more sporting bent? Perhaps, though there's a suspicion a Panamera might be a little less tough.
Above about 30mph or so, concerns evaporate. At motorway speeds the stability is faultless, refinement superb and the powertrain near-perfect, happy to delve into bountiful torque reserves rather than shuffle down the nine-speed gearbox. Still, when it does that, the gearchanges are swift and decisive, and the commensurate jump in performance is huge. All too soon the thought of flying home seems terribly inconvenient; the prospect of 564 miles in a GT 4-door sounds like bliss.
If anything, the big Benz is even more likeable on a twistier road. The E63 is no blunt instrument, yet the GT takes its dynamism up markedly. The suspension and steering work mean the car is both more composed and communicative than the other four-door 63, but it's the four-wheel steer - first seen on the AMG GT R, don't forget - that has the biggest impact. While always feeling natural and consistent, the GT is more direct, more nimble and more accurate than an E63 has ever been, never falling into the occasional 4WS trap of trying to contrive something that isn't there. The tech doesn't attempt to convince the driver that the GT is a substantially smaller car; instead it simply contributes to a feeling of immediacy and immersion seldom seen in something this big.
On the fast, flowing A-roads near the Cairngorms National Park, indeed even on the smaller roads around there, the GT 63 is immense; there's trust in the precision of the front end and the traction of the rear (albeit with a rear-driven balance to the 4WD certainly apparent), unimpeachable body control, powerful brakes and all the V8 thunder you could ever desire. Comfort mode with the exhaust on actually works well as a catch all setting, though there's something addictive about the intensity and aggression of the sportier settings, particularly with a ride that's not as punishing as expected. If your conscience can live with two tonnes and five metres of what feels like a four-wheeled destroyer doing its thing in public, then go for it - there are few more caddishly mischievous (yet hugely entertaining) ways to travel.
Then, seamlessly and as required, the GT can (mostly) settle back into executive express for whatever task is next. The duality is the key to this 63's charm and appeal, delivering both extra luxury and a hit of additional dynamism over the equivalent E-Class; just how broadly talented that car is shows what an impressive display the GT has put on. Whether it's worth so much more will ultimately be up to buyers to decide, though there's absolutely no denying that a 600hp, £95k E-Class would feel like a tangible step down in performance, excitement and sense of occasion after this - it really is that good. For those in the fortunate (and rare) position where a near-£150k four-door coupe is a viable prospect, don't do anything without driving a Mercedes-AMG GT 63 S 4Matic + 4-door Coupe - the name might be confusing, but the car itself is absolutely compelling.
SPECIFICATION - MERCEDES-AMG GT 63 S 4-DOOR COUPE
Engine: 3,982cc, V8, twin-turbo
Transmission: 9-speed 'multi-clutch' transmission, 4Matic+ 4WD
Power (hp): 639@5,500-6,500rpm
Torque (lb ft): 664@2,500-4,500rpm
Top speed: 196mph