Petrol power might seem to be the natural choice for a BMW 6 Series, but once you've experienced the 640d's creamy power delivery and mechanical sophistication, it's obvious why a diesel should top the discerning buyer's wish list.
The straight-six 3.0-litre engine generates a mammoth 465lb ft of torque and 309bhp. Unleash the full force of these numbers and the 640d will cover ground at an astonishing rate.
Here's the real nub of the matter, however; drive more considerately and the 640d will return 51.4mpg (the six-cylinder petrol version's best is 36.2mpg). What's more, the 640d's super-low 144g/km of CO2 output places it in an unbelievably low 22% tax band for company car drivers.
Inside, the 640d is every bit as stunning as its lofty price would suggest. It all feels very special and extremely high-tech, thanks to the lustrous quality of its fixtures and fittings, and the sophistication of its advanced infotainment systems ñ even if some of the dashboard layout and switchgear are seconded from lesser BMWs.