With a power-to-weight ratio of 294bhp per tonne, the 1595kg GT Roadster can hit 62mph in 4.0sec and reach a top speed of 188mph, which is just 1mph down on the GT Coupé.
This is 0.3sec and 8mph down on the considerably more expensive GT C Roadster, and it's also in the shadow of the F-Type SVR Convertible, which has official figures of 3.7sec and 195mph respectively.
You can forget the headlining performance figures, though, because the GT Roadster’s main attraction is its broad spread of ability. Its engine, for one, has plenty going for it, not least deliciously accessible low-rev flexibility. In Comfort mode, the strong torque and excellent part-throttle responsiveness of the lightly upgraded V8 provide marvellous low-rev tractability and easy driving around town.
But in Sport Plus mode, its true potency is revealed. Throttle response is outstanding, and there’s next to no turbo lag as you unleash its reserves in full, with power growing progressively and in a very linear fashion from not much more than 2000rpm all the way to its 7000rpm cut-out. All this endows the GT Roadster with captivating in-gear qualities and a heady rush of acceleration.
Backing up the sheer strength the engine is the rapid-fire gearbox, the overall shift speed and inherent smoothness of which have been vastly improved, especially at higher engine speeds in manual mode, over those of earlier incarnations of the Getrag unit in the GT coupé. This broad scope of driving attributes is very much part and parcel of the GT Roadster’s appeal. One minute, it’s a consummate boulevard cruiser, and with the mere turn of a dial, it becomes a rabid mile-eating supercar.
With the optional AMG Performance exhaust system, as fitted to our test car, it’s not short of aural drama, either. In Comfort mode, there’s an enticing baritone pulse to the exhaust, which grows increasingly more urgent and louder as the revs rise. Switch to Sport Plus, which opens flaps in the exhaust system to increase its volume, and the already serious sounding exhaust note immediately becomes more aggressive and vociferous, with a prolific and all-enveloping bass-driven blare under throttle that is interspersed by rapid crackles on the overrun.
Happily, the lack of a roof structure has done little to spoil the GT Roadster's handling qualities, or its inherent liveliness. In Sport Plus mode, it turns in to corners with the same engaging enthusiasm as the GT coupé. The variable ratio steering lacks the rear-steer function of the GT C Roadster, but it's still extremely direct, quite weighty and pleasingly communicative.
This, and the exceptional grip from the standard Michelin tyres, makes the GT Roadster corner in a determinedly neutral fashion. Yes, it is 50kg heavier than the GT coupé, but the added weight has done little to alter the ability of the front end to hold its line when approaching a tight apex.
Push hard enough and it will understeer, but the limit at which the generously profiled front tyres relinquish their purchase is very high. A well-timed lift of the throttle can get you some manageable tail-out when the electronic stability control (ESC) system is switched to one of its more spirited settings, or you can simply adjust the line by trimming the throttle mid-corner before relying on the terrific traction from the rear and the standard mechanical locking differential for stomping exiting speed.
The GT Roadster sports suspension with fixed rate damping, but it can optionally be specified with the AMG Ride Control set-up with adaptive damping that comes as standard on the GT C Roadster.
The standard suspension is outstanding given the standard of performance on offer. Bump absorption is well controlled, with ride quality being satisfyingly compliant in Comfort mode. It does become a little harsher when you ask for the added body control of the Sport and Sport Plus modes, but that's to be expected.
The brakes are massively powerful, with a lovely pedal feel and excellent resistance to fade.
But what of the drawbacks brought on by the adoption of the soft-top roof? If there is a loss of structural integrity, it is rarely, if ever, felt. You can drive the GT Roadster all day without detecting any real scuttle shake, even on poorly surfaced and undulating roads. The GT Roadster doesn't quite match the GT coupé for outright cornering prowess or overall ride control, but it isn’t likely to disappoint or turn off anybody who already has their heart set on buying one.
With the roof down, windows up and the small plastic wind deflector erected between the roll-over bars, there is fair bit of wind buffeting inside. Raise the roof and it is almost but not quite as cosseting as the GT Coupé. As with lesser Mercedes-Benz open-top models, the GT Roadster can also be ordered with the AirScarf system, which uses a vent mounted within the headrests to project warm air to the neck of the driver and passenger in three levels of intensity.