Originally Posted by Superspeed
It's a matter of taste of course. I would go for the M-kit. It's relatively discrete, blends perfectly in with the general design, in the same time it gives the car a slightly more aggressive look.
If your car has got the adaptive chassis, that's all you need, unless you want to lower the car. If it has the standard chassis I would consider installing a sport suspension. To me it would depend of my driving scheme. If close to 100% urban traffic I would keep the confortable standard chassis. If you go for a spin outside city or even take longer journeys from time to time, I would seriously miss a sporty setup if I were you (unless you've already got the Adaptive Drive option).
The car is fast, but not brutally fast as the 650. Allthough acceleration figures are not that different. I guess the difference in torque is more important. Before you consider an ecu upgrade, get familiar with the car as it is.
I don't miss any extra power in my 640i, but that's just me!
I have decided to go with the M kit, only thing I have to buy it from an after market dealer as BMW today told me that the factory will not supply the kit unless the car comes with the kit from the factory, only for the 6 series. The rims I can buy from them. the car does come with the Adaptive drive, however there are M shocks for the 6 which I might pick up.