ZWARTKOPS, Gauteng – As insignificant as it might seem when viewed on paper, the 45 mm worth of additional ground clearance that the new Mercedes-AMG GLC63 S offers when compared with the C63 sedan with which it shares a platform certainly plays on the mind in the moments before turning into one of the fastest corners on the technical Zwartkops raceway outside of Johannesburg. The global demand for SUVs and the suitably raised driving position they generally offer is also doing little to help my recently consumed breakfast settle in my stomach.

And yet, despite dimensions and mass measurements that suggest otherwise, there’s enough surefootedness, precision and braking ability offered in the newest member of Affalterbach's SUV family to allow me to focus on my racing lines and lap times instead of worrying about steadying my balance in the driver’s seat.

As if to single-handedly quell any suggestion that Mercedes-Benz may have cut corners when it comes to introducing its latest performance SUV, both the new GLC63 S SUV (as it is distinguished) and its GLC63 S Coupé sibling share the brand’s suitably imposing Panamericana grille with their AMG GT cousin. Compared with standard GLC and GLC Coupé, the most powerful derivatives to date (only the "S" version of each will be offered in South Africa) feature 41 mm wider front tracks (32 mm at the rear) and ride 24 mm closer to the ground.

Subjectively, I prefer the slightly subtler styling of the SUV, including its black wheelarch extensions and generally cleaner lines compared with those of the swept-back Coupé, though perhaps those looking to make a statement might fancy the somewhat ungainly pronounced wing and calf-muscle-punishing extended runner boards fitted to the smaller version. Standard 20-inch alloy wheels complete the package. Interestingly, while both options boast identical claimed performance figures (including a 0-100 km/h sprint time of just 3,8 seconds), it’s the Coupé that weighs closer to the two-tonne mark (1 940 kg) than the SUV.

Both GLS63 S models feature uprated performance brakes (390 mm ventilated discs up front) with carbon-ceramic items available as a cost upgrade.

Not as modern in its workings nor layout as Benz's latest offerings (including the E-Class and forthcoming A-Class), the interior of the most expensive GLC models are nevertheless lifted above ordinary by way of standard sports seats and a fantastic AMG-crafted steering wheel. As with other Affalterbach-sourced models, an optional Edition 1 interior package adds further enhancements and customisation.

A member of the C-Class family by name, the drivetrain of the GLC63 S is largely borrowed from the larger Mercedes-AMG E63 S. Indeed, while in this application the twin-turbocharged 4,0-litre V8 engine is tuned to deliver 375 kW and 700 N.m of torque between 1 750 and 4 500 r/min, similar to the E63 this grunt is channelled to all four wheels via the brand's impressive 4Matic+ all-wheel-drive system and the slick workings of a nine-speed automatic transmission. Able to send up to 50% of available torque to the front wheels when required, this system also incorporates an electronic limited-slip differential on the rear axle (non S versions use a mechanical item). Unlike in the fastest E, there’s no drift mode offered in the GLC63.

By way of managing both expectations, those aforementioned dimensions and masses and the level of driving skill that the average SUV owner is likely to possess, the stability control systems incorporated with one of the most powerful family transports on the market have sensibly be tuned to intervene somewhat earlier than a more spirited driver might anticipate. That said, in spirit of modern AMGs, a variety of driving modes (ranging from Comfort all the way to Race) allow the GLC63 S owner to configure any number of variables, including adaptive air suspension, steering weight, exhaust note and level of stability control oversight, as conditions dictate.

Impressively well balanced and precise on track, the GLC63 S Coupé on its standard 20-inch wheels felt appreciably more refined on road than the 21-inch-clad SUV I swapped into later in the day. That said, and as we’ve found with other Mercedes-Benz products of late, the upgrade to a larger-than-standard wheel size not only (more than expected) negatively impacts ride comfort, but also, by default, challenges the integrity of the cabin’s build quality.

Certainly more so than the focussed C63 S siblings (sedan and coupé) and, indeed, more than the brutal E63 S, the new GLC63 S is the AMG model that currently offers the most convincing dual personality. With its signature burbling exhaust note not as pronounced (read less antisocial) as in the C or E, the GLC (on its standard wheels) is more than capable of cruising at 120 km/h in ninth gear (at around 1 750 r/min), before kicking down to the appropriate cog and attacking the horizon with serious purpose should the need arise. The fact that this SUV, in particular, also offers comfortable accommodation for up to four passengers and their luggage only adds to the appeal...