It’s the four-door coupé version of BMW’s M6, which will debut at the NAIAS Detroit Motor Show in January. Powered by the same 552bhp twin-turbocharged 4.4-litre V8 engine as the M6 Coupé, M6 Cabrio and M5 Saloon, BMW now offer a 5/6 Series-based M car in every format except a Touring version.

Blame Mercedes, Porsche and Audi for the proliferation of M versions, the previous V10 model was available in just Coupé and Cabrio, but with the success of Mercedes’ CLS63 AMG, Porsche’s Panamera Turbo and Audi’s forthcoming RS 7, there’s clearly a market for a high-performance 4-door coupé and BMW has one of the best looking platforms available with its Gran Coupé.

BMW has confirmed a German market price of €128,800 when it’s launched next May, which compares with €124,000 for the M6 Coupé (£93,820 in the UK) and €131,400 for the M6 Cabrio (£99,020 in the UK).

A 4-door M5 Saloon is priced at €103,300, which means the M6 Gran Coupé will set you back 25% more than its functionally similar sibling. Expect to pay around £97,000 for the M6 Gran Coupé when it launches in the UK.

*UPDATE (14/12/2012): BMW UK has announced that the M6 Gran Coupé will be priced at £97,490 when it goes on sale from 25 May, 2013.

BMW M6 Comparison - Front and Rear

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BMW M6 - Side Profile

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BMW M6 - Overhead

Aesthetically the M6 Gran Coupé features the same M division upgrades as the Coupé and Cabrio, with the front of the car dominated by large air intakes, optional Adaptive LED Headlights and an M kidney grille.

BMW has managed to carry over the carbon-fibre roof panel (as featured on the Coupé) including the dynamic recess in the centre of the roof. The 4-door coupe is further distinguished from its 2-door sibling by its rear doors and 113mm longer wheelbase – the same as the M5.

Prominently flared wheel arches draw the eye to a track width specific to the BMW M6 Gran Coupe, while it is fitted as standard with unique 20-inch M light-alloy wheels and BMW’s Individual High-gloss Shadow Line package.

With an unladen (EU1) weight of 1950kg the M6 Gran Coupé accelerates from 0-62mph in 4.2 seconds, reaches the kilometre in 21.8 seconds and achieve a top speed of 191mph when delimited.

This compares with 1925kg for the M6 Coupé, which is quoted with the same 0-62mph time, is 0.1 seconds quicker over the standing kilometre and achieves an identical top speed. The M6 Cabrio weighs 2055kg, covers 0-62mph 0.1 of a second slower and the standing kilometre in 22.1 seconds.

The M6 Gran Coupé’s average fuel consumption is quoted as 28.5 mpg with a combined CO2 figure of 232g/km.

BMW M6 Gran Coupe - Interior

So, is there still a business case for the M5?

Mercedes manage to sell both CLS63 AMG and E63 AMG models concurrently, but then a significant proportion of the E63 AMG’s sold are Estates. Perhaps that’s the next step for BMW’s M5. In a range with so many variants, the numbers might not prove as compelling for BMW if the Gran Coupé steals buyers from the M5.

In many respects I hope that’s true, because BMW might then finally decide to build an M5 Touring.