No need for too much preamble here. Clearly it's a 1319hp Walrus-rut, with tusks and bellowing and the blood of your rival plastered across your chest. Nothing advertises hubris more succinctly than a large, extremely powerful German grand tourer and any car park containing both the Porsche Panamera Turbo S E-Hybrid Sport Turismo and Mercedes-AMG GT 63 S is four-and-a-half tonnes to the good in Teutonic two-finger salutes. Both are five metres long. Both will whisk you from Stuttgart to Berlin in 12 parsecs. Both cost around five times the national average salary.
Neither, though, feels particularly long for this world. The GT 63 S, with its 639hp 4.0-litre twin-turbocharged V8, comes with the same countdown clock you'd find draped around the cooling tower of a coal-fired British power station. The engine is cutting edge, and the 257g/km CO2 emitting from its tailpipes a triumph considering the monstrous output. But when the environmentalists finally come for the motor car, the notion of a near £150k, 98-octane-chugging 4-door Coupe will be their poster child. Technically, you might reasonably call it a masterpiece. Conceptually, though, it's a dinosaur.
Which ought to make the plug-in E-Hybrid variant of the Panamera Sport Turismo a small mammal on the evolutionary scale. With an electric motor upstream of the gearbox providing the final 136hp fillip in a 680hp billing, it too is vastly powerful - but as with everything else that marries a petrol engine to an enormously heavy lithium-ion battery, it belongs to a Darwinist tangent, like the Haast's eagle or Irish Elk. Big and intriguing, sure - yet ultimately marked for extinction when the prevailing conditions change.
Still, that's for the tar pit of the near-future. Both cars were delivered to us in the present - and in the spring of 2019, you'd have to be made of reactor core graphite not to get a fizz from climbing into either driver's seat with the key in your pocket. Both were dreamt up with the one-percenters in mind - and then built to carry off the duality required of a 190mph GT car. Size, practicality and physical presence, then, are not an issue. The shooting brake version of the Panamera is to a parking space what the Hoover Dam is to the Colorado River: implacable, impassable and, yes, friggin' enormous. Best to walk round it like a megastructure, moving from element to element like a befuddled surveyor.
With the GT 63 S, better to stand back. Way back. The car might be based on Mercedes' stock 'MRA' monocoque chassis - and is therefore closely related to the E63, among others - but AMG has pulled the body far more tautly over its enormous frame. From the right distance, it looks nothing like its relation. In fact, it looks the bomb. Or at least like it might go off like one; which is appropriate when the 'GT' part of the car's badge is intended to summon up a working memory of the spaceframe-boasting, rear-drive sports car that preceded it in AMG's home-brewed line-up.
Inside, the GT influences are more obvious, most prominently in the vast centre console that comes flanked with rocker switches and buttons controlling all manner of dynamic hocus pocus. This is good. The decision to shunt the gear lever back under your elbow to accommodate a track pad-style infotainment controller, less so. Fortunately you'll soon forget the positioning of the former because the latter is so head-in-hands confounding to use. Delicate sweeps of the finger are fine on tablet screens; not so much while you're driving. There were times on test where the GT 63 pictured was one more errantly repeated sat nav destination letter from being driven off a clifff.
The Panamera rounds this problem by making its own large-scale infotainment display a touchscreen. This brings with it its own issues of course, but they are minor compared to the Mercedes. It gets its gear lever in the right place, too, and lets you use it for a bit of sequential shifting if that takes your fancy. Getting things in the right place is the Panamera calling card: you sit lower than in the AMG, with a properly round steering wheel to grasp and proper dials behind it, too. Making sports car ambience seamlessly collide with driver-focused luxury is pretty much what Porsche has been doing for the last twenty-five years, and it shows. The Panamera is as handsome as a marine chronometer and built like a quartz crystal.
The GT 63 S is showier, though, and gets comfier seats. Its most prominent fixtures - the connection between seat and floor, wheel and rack, pedals and bulkhead - don't seem set in quite the same concrete as the Panamera, but its soft-touch trim materials are second to none and we'd rather have Mercedes' proper buttons than Porsche's haptic-feedback switchgear any day of the week. The wolfish bark of the M177 motor on start-up - here in tricked-out, boosted-pressure S format - we'd take twice on Sunday.
Disappointingly, if not unforeseeably, the Panamera makes no sound at all when you push-button it to life. For as long as the 14kWh battery pack has sufficient charge, it will whisk you about noiselessly and without emissions. In E-power mode (assuming you've plugged it in the night before) Porsche claims it will do this for about 22 miles. We didn't, so it didn't. But we let it hasten us out of town and onto a motorway and the most notable thing to record is that Porsche has given it, via adaptive air suspension, a slow speed ride quality to match its muted tones. In passenger cell isolation and rolling refinement, the E-Hybrid is top notch.
Sufficiently so for it to outmatch the GT 63. Despite its own multi-chamber air springs, the big Mercedes has a familiar AMG-fettled tendency to bristle slightly at UK-sized road furniture; not so much that you'd mind in general use, but enough for it to be noticeable when driven back-to-back with the Panamera. Still, it's limited to an about-town sort of lumpiness - merge onto a motorway and it's a completely different story.
We drove the Porsche up to the Peak District and the 63 back. In the smoother, quieter Porsche you tend to drive more economically - not least because there is some drive mode faffing to be done if you don't want to recklessly spill what remains of your battery charge. In its default E-hybrid setting, the Porsche reported 60+mpg; ask it to preserve electricity until you get where you're going, though, and its own turbocharged 4.0-litre V8 will quickly have it going in the wrong direction. Opt to have the petrol engine charge the battery on the move as we did and the Panamera's average drops to 30-something-mpg before you can say "deadweight".
In the GT 63, we averaged around 21mpg on the motorway. Not because the car won't do better than that but because it's hard to resist occasionally leaning very hard on the accelerator just for the sake of it. Do this in the Panamera and you get a binary sort of answer: yes, the 550hp V8 which fills out the 'Turbo' bit of the badge still works, and with some gusto. In the Mercedes you wait a split second longer for the nine-speed auto to register 'full steam ahead', then you fall face first into the kind of almighty, mercurial shove that ought to outlast any sane man's bottle.
Does that make it better on a motorway than the Panamera? Objectively, no. The Porsche is more economical (sort of), quieter, better damped, better insulated, nicer to interact with on the button-pushing front (which is critically important if you're going to spend a great deal of time in it) and faster than you'll ever realistically need it to be. It is also as surefooted as a supertanker at high speed, which is partly to do with all-wheel drive and the hugely thickset way it steers - and partly to do with it weighing nearly as much as a supertanker. But we'll come back to that. For going in straight lines effortlessly, it's very worthy.
The GT 63 requires marginally more concentration. It doesn't arrow up the M1 quite as consistently. Not in soothing ambience, at any rate. In control surfaces though, and response and immediacy, it is plainly superior. The Panamera is at its most pleasing when the hybrid gubbins aren't working at all; unencumbered with such things, the Mercedes delivers this level of interaction all the time. There is no meandering disconnect in the accelerator or brake pedal; the M177 doesn't go AWOL when you lift off (preferring to close off four cylinders instead) and because the responsiveness is unburdened by a battery pack and its ancillaries, it gives the impression that it might go x-rated at any moment.
It is this final, winning attribute that carries it triumphantly onto the Peak District. The nicest thing to say about the Porsche on an empty, dry and well-sighted B-road is that it is absolutely as good as it could possibly be with a 205kg handicap to hustle through every bend. Plainly the extra weight is carried very low and in such a way so as not to sacrifice the sophisticated rear-biased balance of the car (aided in this case by the option of a steerable back axle) - but a 680hp Panamera ought to be as effervescent as a basketball sized Mento dropped into Pepsi-filled roll-top bath. And the E-Hybrid isn't. It's hugely fast despite its underpinnings, not because of them.
It's a wonder then that the quality of the car's bump absorption doesn't abandon it when the going gets tough. The Panamera's body stays obediently flat and the occupants blithely comfortable even under duress. It is tenaciously grippy, too, and communicative enough through the steering and seat backs for you to know it. In fact, the car is handicapped less by the limit of its actual ability than it is by your reluctance to genuinely approach it, lest you make a catastrophic mistake with the unfeeling brake pedal and leave an asteroid-sized divot in the National Trust's hallowed turf.
At 2.1 tonnes, the GT 63 is no-one's idea of light. But it's a baby water boatman compared to the Panamera - if you can imagine such a thing being powered by one of those colossal Yamaha outboard motors. Naturally it's the rapacious V8 which receives top billing in the AMG (in Race mode, it is less a power source than it is a full-scale possession, its latter revolutions inspiring all manner of eye-swivelling, head-spinning paroxysms in its driver) but crucially it doesn't overawe the chassis it's connected to. Compared to the Porsche, the steering is deceptively light and the body control deceptively liberal; yet somehow, whenever it counts, the GT 63 is formidably good.
All-wheel drive, all-wheel steer and a-l-o-t of torque vectoring feature here too, yet in the AMG they have been deployed not to reassure you of the car's heft, but to counteract it almost completely. Focus your attention on the business of going very quickly with the car in any of its more determined drive settings and it seemingly shrinks by two classes. The ride quality barely seems any more stringent than in Comfort, yet it coincides perfectly with the chosen handling characteristic, which is, by turns, poised, accurate, adjustable and remarkably forgiving. Plainly the absence of a lead balloon in its nether region is helping you get the nose turned in quicker and on the throttle earlier, but it cannot account fully for how much faster you drive the 63 - nor for how much more fun you have while doing it. Among very large German saloons - the E63 included - it's hard to think of another quite so well attuned to the more enlivening end of modern GT duties.
The Panamera isn't. Not this Panamera, at any rate. The E-Hybrid is too fast and swish and unsparing in its many qualities for it to be called a necessary evil - but you come out of it only half gratified: unruffled, contented and almost certainly ahead of schedule, yet no more moved than a Eurostar passenger. Granted, there's something to be said for that, and had we tested the car against any comparable hybrid model, it would likely have carried the day. But the second most expensive Panamera is further confirmation - were it needed - that electrification, no matter how extravagant its pay off in powertrain numbers, plays second fiddle to an unfettered combustion cycle.
Mercedes-AMG has again proven itself a master of that process. It is a measure of the GT 63 S's broad appeal that it easily outshines memory of the AMG GT. Affalterbach's sports car was a fine marker for what it could achieve solo given the rub of the green - but it failed to eclipse its closest rivals in the essential business of dispensing raw driving pleasure. In that regard, we have no such qualms about its second album. The 63 is a very pleasant cruiser. A better B-road conqueror. And a rolling thunder generator par excellence. If there is a large luxury saloon with more going for it, we've not yet driven it. A dinosaur, yes. But the best of them.
SPECIFICATION - PORSCHE PANAMERA TURBO S E-HYBRID SPORT TURISMO
Engine: 3,996cc, V8, turbocharged with electric motor
Transmission: 8-speed dual-clutch, all-wheel drive
Power (hp): 680 (combined)
Torque (lb ft): 627 (combined)
0-62mph: 3.4 secs
Top speed: 192mph (86mph EV)
Weight: 2,325kg (DIN)
MPG: 72.4 (WLTP)
CO2: 76g/km (NEDC)
Price: £139,287 (£157,370 as tested)
SPECIFICATION - MERCEDES-AMG GT 63 S 4MATIC+ 4-DOOR COUPE
Engine: 3,982cc, V8, turbocharged
Transmission: 9-speed multi-clutch, all-wheel drive
Power (hp): 639@5,500-6,500rpm
Torque (lb ft): 664@2,500-4,500rpm
0-62mph: 3.2 secs
Top speed: 196mph
MPG: 21.4 (WLTP)
CO2: 257g/km (WLTP)
Price: £135,550 (£146,625 as tested)
Photos: Sim Mainey