While the 640i also comes exclusively with BMW's full-time four-wheel-drive system – xDrive – you've got options with the suspension setup. As standard, the Grant Turismo is fitted with self-levelling air suspension at the rear axle. Adaptive suspension costs £1670 and adds air suspension to the front axle; for your money the dampers will also now be adaptive, meaning the ride height can be dropped 10mm in Sport mode.
For £3340, the Executive Package includes all of the above and adds active roll bars and four-wheel steering, with the respective aims of improving body control and increasing agility.
What's it like?
BMW has massaged the dimensions of the car this one replaces – the shorter, taller 5 Series GT – into something quite a bit more palatable, but to our eyes it remains some way short of even the superb 5 Series Touring in terms of kerbside appeal.
It scores substantially better in terms of rational appeal. At 610 litres, boot space with the seats up is better than that of a 5 Series Touring, and the Gran Turismo is also longer where it matters than its predecessor, matching the wheelbase of the 7 Series. Consider also that the seats are positioned 60mm higher than in a 5 Series what you have is a high-rise machine that's exceptionally commodious and – thanks to its engine – has very long legs.
This six-pot is a known quantity, of course, and is so effortlessly effective that it was always going to slip with supreme ease into a luxurious cruiser like this one. A peak torque output of 332lb ft arrives barely above tickover, at 1380rpm, and remains on tap until the tachometer needle has breezed past 5000rpm.
Short-shift using the paddles, wring it out in Sport mode, crawl through town: marshalled by an eight-speed torque converter whose shifts are as smooth as one could reasonably expect, there's never really a point where this big six isn't wonderfully well mannered.
It's an engine matched by the chassis in some aspects but somewhat beaten by it in others. This car weighs some 115kg (or thereabouts) less than the 5 Series GT. That has brought with it an incisiveness to the way direction changes are negotiated, and while the 6 Series GT never really looks like shrugging off its physical proportions, good body control, nigh-unbreakable traction and all that torque make it remarkably easy to place on the road and work through corners.
It's an inert process characerised by security, however, and one that reflects BMW's positioning of the car as a junior 7 Series. The air springs in particular don't convey much in the way of feel, obfuscating the natural body movements you rely on when pedalling a big BMW saloon.