Not driven a 640d but I suspect it will be ferociously quick but you’d never know due to the lack of “fast” noises, which removes some of the sensation of speed, especially compared to an AMG V8.
I had an Audi A6 Bi TDi which was much the same. I enjoyed driving it because I respected how incredibly capable it was, but I couldn’t gel with it for the lack of sound and sensation.
It was a brief foray into fast diesels. Really wonderful car, beautifully engineered, and really fast, perfect for early morning late night motorway jaunts to the airport, but it didn’t work for me as an engaging car.
The drivetrain is good - the ZF 8 speed unit is brilliant. It's a big lump but reasonably economical. Bit tractorish in urban settings. Effortless when taking the car on cross country A and B roads.
Most on the roads were MSport and there are a few SEs. The differences are trim and some supposed differences to the steering wheel. MSports tended to come with 20" kerb scrapers - the SEs occasionally 18" but I think quite a few were also on 20s.
My complaints ......
- suspension - not refined enough - variable dampers not supplied as standard - the car felt better with three or four in it on some roads
- steering - it has the variable electric power steering which I thought spoiled the car on more interesting A roads when at legal speeds. Pushed round slow corners on summer tyres it would jitter sideways at the back on the Dunlop Maxx Sport. Oddly it felt much better on winter tyres - even though the rear grip was lower.
Also the front seats are the same as the convertible - this means the seat belts are mounted in the seats. When I was alone in the car then the passenger seat vibrated atmotorway speeds which was disconcerting. I think this was down to the rigidity of the floor seat mountings to take the seat belt forces.
The fifth seat position is limited but occasionally useful (but not necessarly suitable for female passengers in short and/or tight skirts).
The car is basically the equivalent of an optioned up 535D from the same era but with a longer and lower body on the same wheelbase. It's just on 5 metres long.
I was initially quite enamoured with it but became rather disenchanted with it after 18 months and counted down the last 12 months until I changed it. It was the steering feedback that eventually got to me - I just stopped enjoying it. For the money I think BMW were lazy - took a 5 series, dressed it up to look better and upped the price, but didn't put much thought or care into making it tangibly better.