In an industry obsessed with the notion of reinvention, it is easy to undersell the significance of the SL’s recent metamorphosis. After all, at face value, the model appears to be much as it ever was – a big, reassuringly expensive roadster powered by an impressively large petrol engine. Sure, it has traded in the folding hardtop for a fabric roof and become a 2+2 as standard, but it still presents as peak Mercedes – a flagship chiefly built to impress friends and intimidate (golf club-based) enemies. Bonkers V12-powered dreadnoughts aside, the SL has cultivated a multi-decade reputation for charioting sun-bleached retirees between engagements. You don’t shed that amount of estimation in an instant. 

And yet repositioning is clearly afoot. Perhaps not in the fundamental, brain-pickling way that has seen an electric SUV declared a Mustang or something from China proclaimed a Lotus, but as soon as the manufacturer announced that the new SL would be exclusively developed and marketed as a Mercedes-AMG product – and built on a bespoke platform, no less – we figured that its days as a mostly benign grand tourer must be numbered. Especially when two of the three available trim variants were confirmed as V8 carriers even as the turbocharged 4.0-litre engine was denied to the reliably thuggish C63. 

This, the new SL 63, is inevitably the chunkier of the two as far as output is concerned. The earlier SL 55 that John drove back in December was furnished with 476hp; the halo model gets 585hp. This is quite a lot more. Torque is up too at 590lb ft (a 74lb ft increase) which is as much as you’ll find in the current Porsche 911 Turbo S, a car that rivals the 63’s inflated price tag. And while Mercedes has been known to twin previous iterations of the SL with even more thrust (the R230 SL 65 Black Series famously boasted 738lb ft of the good stuff), it has declined to offer it in conjunction with four-wheel drive. Now, with the assistance of standard 4Matic, the SL63 is claimed to be 0.2 seconds quicker to 62mph than even the 6.0-litre V12-equipped Black. Find a long enough stretch derestricted, downhill autobahn and it’ll probably nudge 200mph.

But its bragging rights over the SL 55 are not limited to power or straight-line pace. The 63 also gets the latest generation of AMG Active Ride Control, which means it features active anti-roll stabilisation (an hydraulic alternative to the 55’s conventional anti-roll bars) and while both are four-wheel steerers by default, the quicker SL gets a more sophisticated electronically-controlled, limited-slip rear diff. Admittedly, from the outside there are fewer ways to distinguish the SL 63 Premium Plus from an SL 55 Premium Plus than a buyer of the former might hope – especially when you consider its £24,250 premium – but regardless, the latest SL, even on a miserable day, is well worth leering at. It is honed and sleekly alluring in all the places its R231 predecessor was fumbled and forgettable. 

Inside, it’s not quite so well organised – although that might be a symptom of just how much stuff needs organising. Mercedes UK is very conscious of the sheer number of features baked into the current MBUX system, and the S-Class-derived interior is inclined to flaunt its complexity rather than lean toward ease of use. But it’s comforting to be reminded that most of the dynamic functions we’d care about are assigned to the two rotary dials on the steering wheel. This is what you want with six drive modes to cycle through, especially when choosing between them has such a noticeable effect on the driving experience. 

As John pointed out in the 55 – and in spite of the cleverer chassis – the new SL is not inclined to embrace ‘Comfort’ as its best showing. Understandably, there is a sense of AMG wishing to have its cake and eat it: to make the car seem capable of plush, GT-grade waft one minute and hunkered-down horizon assault the next. But the uprated level of intent is hard to disguise in its most laid-back setting, and the 63 is curiously unsettled by uneven B roads – evidently desperate to float along on the additional bandwidth offered by the more liberal anti-roll system, but unable to curate the result into something consistent. It isn’t terminal or even particularly disconcerting; it’s just a drain on your enjoyment. 

Fortunately, ‘Sport’, as it did for the 55, pretty much remedies all these shortcomings. The waywardness at low speed is replaced by a more confident hold on the body, which doesn’t sacrifice a generally well-mannered secondary response to manhole covers and the like. More importantly, its superior assurance chimes with agility that four-wheel steering lends to this generation of SL; this is a big car, but it turns in swiftly and in that all-of-a-piece way that encourages (very) fast progress. The steering isn’t going challenge any stripe of Porsche for feedback, but it’s impressively well geared for task at hand, and reinforces the impression that the 63 is endowed with sufficient smarts for it to flow engagingly through corners. Much as you expect AMG intended. 

Of course, between corners, it’s an ears-pinned, nostril-flared hot rod of the first degree. Sadly, the weather didn’t allow for any roof down action, but if the sound coming through the hood is anything to go by, you’re not going to want for rich, V8-toned goodness in the 63. Whether or not the SL needs all the performance it keeps on tap from virtually any engine speed is a question for another day: the short answer here is that it doesn’t seem overwhelmed or at odds with the additional power. Quite the opposite. AMG’s fingerprints are all over its high-speed fidelity. Here, finally, is an SL built from the ground-up with 200mph in mind, rather than it seeming like a grafted-on hypothetical. 

Whether or not that is as it should be is also open-ended. Mercedes appeared to be floundering with the model’s identity when it became the SL-Class and began disappearing from most people’s radar – yet apparently it still found favour with some customers as a plush, wig-ruffling grand tourer. While Mercedes-AMG has obviously been instructed not to throw out the baby with the bath water, the new SL has manifestly exchanged some of that affable character for something more purposeful, and the 63 is at the zenith of its interpretation. The impending appearance of a next-generation GT means the flagship retains its size, practicality and unrepentant heft regardless – but it isn’t necessarily the car you’d choose to waft around the countryside in while your pension pot swells. No, it’s much, much better than that. 

Engine: 3,982cc, V8, twin-turbo
Transmission: nine-speed auto, four-wheel drive
Power (hp): 585 @ 5,500-6,500rpm
Torque (lb ft): 590 @ 2,500-4,500rpm
0-62mph: 3.6 seconds
Top speed: 195mph
Weight: 2,048kg
MPG: 21.4 (WLTP)
CO2: 299g/km (WLTP)
Price: £171,725 (as tested, £173,325)