It's the second M car to get the very highly pumped 4.4-litre twin-turbocharged V8 engine and therefore boasts 552bhp and 502lb ft of torque. That's more power than the Jaguar XKR-S. Power, naturally, goes to the rear wheels via a seven-speed M double clutch gearbox with launch control.
As such, BMW quotes a 0-62mph time of 4.2 seconds for the Coupe, and 4.3 seconds for the Convertible, 0-124mph in 12.6 seconds (13.1s for the drop-top) and the option of a 189mph top speed with the ‘M Driver's Package'.
Despite this herculean power and acceleration, BMW still reckons the Coupe will return 28.5mpg, though we suspect anyone achieving this hasn't really got the point of a twin-turbo V8. There's a carbon-fibre reinforced plastic roof for the coup', start-stop, and other Efficient Dynamics stuff, which brings CO2 emissions to 232g/km (239g/km for the convertible).

There's an M differential between the rear wheels for better traction and stability during "dynamic lane changes and accelerating out of corners", and as expected, you get the full menu of dynamic damper control, DSC, lightweight brakes (with an option for M carbon-ceramics), and the customary Big Fat Button Of M, to call up previously stored car setup configurations. Set it to maximum and then sellotape it.

The Big Six gets a modelled lower air intake, flared arches - to compensate for the 30mm extra track width over the standard car - M gills, a rear apron with diffusers, twin exhausts and 19in wheels. 20s are an option. Inside, there's lots of M badging, some leather, carbon fibre strips, illuminated sills and some digital assistants including lane departure warning, surround view, night vision with pedestrian recognition (do you really need a computer to tell you what a human looks like?) and Internet access. 

To aid your ruminations, consider the price: the Coupe costs £93,795 and the Convertible costs £98,995. Both will go on sale in the UK on 15 September 2012.