What is it? A seriously quick Mercedes-Benz E-Class built with the express purpose of snatching the bragging rights from BMW's much-heralded M5.
If the previous 6.2-litre model's E63 badging was a bit misleading, then this latest version of the Mercedes super-saloon is verging on libellous, because it's powered by a 5.5-litre twin-turbo V8.
The confusion doesn't stop there, either, because the engine is available in two states of tune. For the best part of 75,000 you get 518bhp, but pay 6495 more and AMG will ramp up the turbo boost pressure to deliver an M5-rivalling 550bhp.
It was the latter that Mercedes sent us to try on UK roads.
What's it like to drive? The AMG's performance is every bit as impressive as the figures suggest, even if it's not delivered as efficiently as in the M5, which makes its 552bhp from just 4.4 litres.
To be fair, the Merc's larger engine means it beats the BMW's 502lb ft of torque, producing 516lb ft in standard guise and a whopping 590lb ft in our tweaked car.
It's that torque delivery that helps the Mercedes punch through the air a shade quicker, hitting 60mph in just 4.2 seconds the M5 take 4.4 seconds.
Where the two cars really differ is the way they assault your senses. While the M5's engine is turbine smooth, the Merc is more of an old-school muscle car, bellowing out a languid V8 baritone exhaust note even when you're just pottering around town.
Not that there's anything languid about the handling. With a wider wheel track than the standard E-Class, a bespoke steering rack and three different settings for the adaptive suspension, this AMG model is surprisingly agile and communicative for such a big car.
Find yourself taking too much speed into a corner and the massive carbon ceramic brakes fitted to our car a 9300 option scrub off speed like you've driven into a swimming pool.
Such is the predictable nature of the handling that even with all the electronic traction aids switched off, you feel 100% under control. For such a focussed car the ride is impressively smooth, too.
What's it like inside? For the most part the AMG's interior is similar to those of more mundane E-Class models; solid, without being particularly inspiring.
There's plenty of space for four five at a pinch while the quality of the materials and the standard of construction are first rate.
There's also plenty of standard kit. Notable highlights include a full leather interior, AMG sports seats and a neat Alcantara and leather steering wheel. Annoyingly, though, while it looks and feels great, the wheel is offset to the left, so you too often find yourself banging your elbow into the centre console.
Should I buy one? If you're in the market for an E63, then chances are you'll have one eye on the BMW M5. So, which should you choose?
On the one hand, the AMG's delightful guttural sounds, its engaging mechanical interaction and its ability to deliver almost as many thrills at real-world speeds as it does when maximising its awesome performance makes it an intriguing proposition.
By comparison, the M5 feels rather clinical and you need to be carrying some serious speed to make it really come alive. That said, the M5 is the more technically advanced car. As well as delivering a stupendous turn of speed, it's incredibly poised, refined and comfortable. What's more, it's a big chunk cheaper than the E63, so it gets our vote - but only just.
What Car? says