You’ll be able to buy your 6 Series GT with one of two petrol engines (the four-cylinder 630i or six-cylinder 640i) or a single diesel, the 630d, which is likely to be the best seller.
The 640i is a turbocharged 3.0-litre unit that is unlikely to find many homes in the UK, but not because it isn’t a nice companion. It’s certainly powerful enough, with 335bhp on tap and superb low-down pull to dispatch slow-moving traffic, and it’s also impressively smooth, even when pushed hard. BMW’s standard eight-speed automatic gearbox works well, too. No, the problem is fuel economy; the 630d will go much farther on a full tank and emits less CO2.
The 630d is no slouch; it’ll crack 62mph from standstill in 6.1sec, less than a second behind the 640i. Yet, the reason the 630d is our pick isn’t just its outright pace; it’s the way it pulls harder from low revs, making it feel more flexible in everyday use. In addition, it’s right up there as one of the smoothest and quietest diesels in the class, if not the best – we rank the excellent 2.9-litre diesel in the Mercedes-Benz CLS above it.
So, the 6 Series GT’s pace is good for overtaking and sprinting down motorway slip roads, but it’s no sports car come the corners. All 640i models come with BMW’s xDrive four-wheel drive system as standard; it's an option on the 630d, too. With it, you rarely find the wheels struggling for traction, but the car’s sheer size makes it feel less eager to change direction than a 5 Series. That’s the same even if you add other options designed to aid handling, such as self-adjusting anti-roll bars, and select the sportiest driving modes. The 6 Series GT’s steering, too, isn’t particularly feelsome in any driving mode. Ultimately, both the CLS and Audi A7 Sportback manage to feel more agile.
As standard, the 6 Series GT gets self-levelling air suspension at the rear only, but we have yet to try this set up. With the optional all-round air suspension fitted, while the car still doesn't match the soothing ride of an A7 (also fitted with air suspension) at motorway speeds, it is much more settled than a CLS. Around town, it's even better, to the point where the 6 Series GT rides nasty lumps and bumps better than most of its rivals, including the A7.
And along with the smooth six-cylinder engines, the 6 Series GT's interior makes for a seriously relaxing place in which to spend time at speed. Sure, there's a bit more wind noise than in the CLS and a touch more road roar than in the A7, but in both respects it is restrained enough to be a fantastic mile-muncher.