New car? Or facelift?

Mercedes-AMG has waited until the GT v1.5 to unveil the convertible version, complete with dramatic new Panamericana-inspired 15-louvred grille, active air management and, on the GT C, active rear-wheel steering and an electronically locking rear diff.

In the right spec – Magno grey with the red soft-top, for example – this thing looks unequivocally awesome. It’s an important point: the visual drama is a huge part of the deal here, possibly even more than absolute dynamic prowess.

Really? Remind us where the Mercedes-AMG GT C fits in the grand scheme of things.

The top-flight GT C, frankly if you’re scoping out this sort of territory you’ve probably got that default other car as your daily user: the Range Rover. Still, let’s assume everyday useability and at least some degree of entertainment matters.

The Audi R8 V10 Spyder, doesn’t just go, stop and handle sublimely, it does it with an atmospheric engine. The current car is a brilliant all-rounder, although weirdly the vastly cheaper TT has a better – and roomier – cabin. Then there’s the Bentley Continental GT convertible, which is close on power to the AMG GT C but costs more.

Or the Ferrari California T, an even more glamorous player that doesn’t share its badge with a hot hatch. You could lob in Jaguar’s F-Type as a bit of a left-field choice, but in SVR form it’s actually good enough to mix it in this company. Or, for the ultimate grudge match, there’s the Porsche 911 Turbo S convertible. That’s what Thor and his mates drive on Asgard.

How’s AMG progressing as a standalone car manufacturer?

Following the SLS, the GT was only the second solo AMG outing, a ground-up, clean sheet car done wholly in Affalterbach. where the emphasis, we suspect, is on the engine rather than chassis.

As much as we enjoyed the GT coupe, it’s a right old handful when you start going for it down a typical British B-road. If you thought the roadster might dial things back a bit, think again.

Five minutes up the road – a very smoothly surfaced American one – and this already feels like a car that takes no prisoners. The throttle has a hair trigger, and those 549 horsepowers are in-yer-face. It’s a home-grown German hot rod.

Not a lily-livered poser’s convertible, then.

Certainly not. There can’t be many soft tops out there as rigid as this. The GT coupe’s lightweight aluminium spaceframe also receives extra reinforcement to counter the effects of decapitation.

New side skirts with chunkier walls and extra chambers are added, while the dashboard gains additional strut braces against the windscreen, and there’s another tower brace between the soft-top and the fuel tank.

A cross-member behind the seats also boosts the rollover protection system. Upfront, the GT C Roadster uses magnesium in its structure to reduce inertia ahead of the axle, enhancing turn-in.

The roof mechanism is also trick: a magnesium/steel/aluminium structure supports a three-layer hood, available in black, red or beige, which opens or closes in 11 seconds at speeds up to 48km/h.

How does it feel behind the wheel?

Like it means business. Serious, making-you-an-offer-you-can’t-refuse sort of business. The muscle car hot rod equation is amplified by the driving position. There’s such an expanse of bonnet visible through the windscreen you could apply for planning permission – for a shopping mall.

The GT C’s cabin ambience is enlivened by nappa leather trim, an AMG Performance steering wheel, and a thumping Burmester surround sound system with a fully integrated sub-woofer. The rear axle isn’t quite directly beneath your back side, but it’s close, and that sensation informs the driving experience.

The GT C is also wider at the rear than the standard car (2007mm v 1939mm), and uses bigger wheels and tyres (305/30 R20 v 295/35/R19).

Its rear apron has wider contours and extra vents for improved airflow, although both models feature a boot-lid made of SMC (Sheet Moulding Compound) and carbonfibre with an integral spoiler, to help reduce weight (the regular roadster weighs 1,670kg, the C 1,735kg).

On a scale of one to ten, what are we talking in terms of sensory overload?

Oh, 11. The engine truly is a force of nature, somehow squeezing out 549hp and 502 torques against an exhaust note that makes Brian Blessed sound like Joe Pasquale, while serving up a 315km/h top speed and 0-100km/h time of 3.7 seconds – with 259 CO2s.

The GT C uses AMG’s triple-mode Ride Control adaptive damping system, so you can flip between Comfort, Sport and Sport Plus for progressively less compliant rebound and compression levels depending on how masochistic you’re feeling.

The C also adds a Race mode to the Dynamic Select dual-shift transmission menu, to go with C, S, S+ and Individual. First gear on the seven-speed DCT – a rear transaxle job – has a higher ratio, while seventh and the final drive are lower for greater urgency.

It also has bigger front brakes (390mm v 360mm, with ceramics as an option on both GT and GT C). This is a convertible that clearly has designs on a racing circuit or track days, but how many soft-tops do you see hammering round Bedford Autodrome or Silverstone?

And how does it fare against those rivals you mentioned above?

The AMG has fantastic turn-in, and the active rear axle reduces understeer and sharpens agility appreciably by pointing the wheels 1.5° in the opposite direction to the fronts up to 100km/h. Even so, it still can’t help but feel nose-led compared to the mid-engined Audi.

The Porsche Turbo isn’t the best 911 in terms of absolute feel, but its steering, AWD traction and braking are superhuman. And it ain’t slow, either. The Ferrari’s too soft, but even a soft Ferrari is still a Ferrari. The Bentley’s too heavy, the Jaguar a secret gem saddled with an inferior interior.

The GT C roadster feels approachable at, say, six-tenths, but turns a bit sledgehammer the harder you go. An extremely exotic sledgehammer, but still. Ultimately, it’s not quite as polished as it could be.

Is the less powerful version worth a look – should the old bonus roll in or my lottery numbers come up?

Actually, yes. Switching into the 469hp GT roadster is a textbook case of less being more. But it also rides more comfortably and fidgets less, and while it doesn’t warp off the line quite as flamboyantly as the GT C, you can probably live with the three-tenths it gives away to 100km/h.

AMG sold close to 100,000 cars last year, and its fanbase generally isn’t backwards about coming forwards. In this case, though, we’d settle for 81hp less.