The SL range expansion gathers apace as AMG adds a second model above the V8-engined SL 63 AMG with the introduction of the bi-turbo V12 SL 65. Taking the lunacy dial and turning it up to 12 AMG's 6.0-litre bi-turbo SL delivers 630hp, though it's the 1,000Nm of torque available from 2,300- to 4,300rpm that's the real draw.

Able to reach 62mph in a tyre and traction control testing four seconds the SL 65 AMG achieves 125mph in 11.8 seconds. That's still some 3.3 seconds slower than Ferrari's new F12 Berlinetta so expect a Black Series in time to address that. The Merc's top speed is pegged electronically at 155mph - though without it 200mph shouldn't be too much trouble.

Sitting at the top of the SL range the SL 65 AMG has always been a tiny-number model, appealing to a specific audience. Its positioning now looks even more incongruous given the existence of the SLS AMG Roadster - which it outguns on output (630- against 571hp) if not quite on performance.

As ever, and no matter how uncomfortably it fits with the car's core appeal, economy is improved. The SL 65 AMG can achieve 24.4mpg on the combined cycle, which is some 17% better than the car it replaces thanks in part to a standard stop-start system. Try achieving that figure in the real world and you'll be disappointed.

You won't be underwhelmed by the noise it makes though, with AMG promising a rousing soundtrack thanks to a newly developed exhaust system. This not only breathes freer, but is thinner walled and significantly lighter. Quicker gear shifts are promised too via AMG's four-mode Speedshift plus 7G-Tronic automatic, the transmission also going some way to improving economy thanks to low friction internals.

Unique AMG styling, further developed suspension and all the kit you'd be ticking option boxes for further down the SL range come as standard. They should too, as although there's no pricing yet revealed don't expect much change from £160,000 - if any at all.

Kyle Fortune - 20 Mar 2012