[Digi]

The M3 has a completely different tranny, so it may let you get the user-interface and general technique down, but it will not shift the same at all as an M5.
A regurlar 5 series should give you a good estimate of space and size.

 

[Digi]

How hard is it to get used to the iDrive? Can you customize it?

My brother's wife figured it out the first day, and she is techno-illiterate. I think it is something that once you get it, it is easy. The question remains if it isn't intuative and distracts the driver more than normal controls -- it shouldn't be in a BMW. I think it isn't hard to figure out, it is just "why?" technology.