The Gran Coupe is the most convincing M6 yet, and the extra space demands no sacrifice in performance or economy. The hi-tech 4.4-litre engine gives incredible pace, yet the equally practical M5 is £24,140 cheaper. The stylish Mercedes CLS 63 AMG has a similar price advantage, and the Gran Coupe simply isn’t worth such a large premium.

With high-performance grand tourers like the Porsche Panamera Turbo on sale, and Audi set to launch the RS7, BMW was never going to be far behind. So here’s its offering: the M6 Gran Coupe, which joins the existing Coupe and Convertible models.

At first, the idea of fitting two more doors to the M6 might not make much sense – that’s what the M5 saloon is, in essence. But with a 113mm longer wheelbase, a slightly more luxurious cabin and the option of five seats, the M6 Gran Coupe is definitely different.

BMW describes it as the most sumptuous M car yet, and the leather interior attests to that. But while there’s decent rear legroom, headroom is a little tight. Anyone sitting in the middle seat will have to straddle a centre console, too, which explains why BMW officially calls this car a 4+1-seater.

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Despite the extra length, it’s hard to tell the Gran Coupe apart from the standard M6. The compact rear doors are integrated neatly into the muscular design and familiar performance cues like the huge air intakes in the front bumper and forged 20-inch alloys ensure that it looks every bit as purposeful as the coupe.

It’s just as imposing to drive, with all the brute force we’ve become accustomed to from the familiar 552bhp 4.4-litre twin-turbo V8. This engine debuted in the latest M5, but the astonishing way it delivers its power still catches you by surprise. Throttle response is razor sharp, and with nearly 700Nm of torque at your disposal from low in the rev range, it’s alarmingly easy to see three-figure speeds appearing on the head-up display.

You won’t be sacrificing any performance by opting for the more practical Gran Coupe over the standard M6, either; both claim an identical 0-62mph time of just 4.2 seconds. Fuel economy and CO2 emissions remain the same, too, at 28.5mpg and 232g/km.

Every part of the driving experience can be tailored to suit different demands, including the speed of the dual-clutch seven-speed gearbox’s shifts and the settings for the active dampers and speed-sensitive steering. That means the Gran Coupe can switch from softly sprung cruiser to snarling sports car at the press of a button.

In the most aggressive Sport+ setting, the traction control is dialled down and the steering is lightning fast. But in any mode, the Active M Differential splits power between the rear wheels, giving a level of agility and surefootedness you don’t expect from such a big car. Unlike some performance coupes, it always rides well, too.

It’s not all good news, though: the quad exhausts never make more than a muted roar and the Gran Coupe can feel numb and uninvolving. In that sense, it’s short on drama – it rarely feels as exciting as a £100k supersaloon should. Plus, there’s a number of cheaper rivals, like the £80k Mercedes CLS 63 AMG, to consider.