Hi,
Based on Booster's pictures and experience, I went with the M3 wheels as well (without spacers and with stock Pirelli 225/45 and 255/40):
The car is lowered on KW V1 suspensions and it rubbed a lot in the rear wheels arches under compression (on the middle of the tire's sidewalls!).
I doubt I can use bigger tires, as Booster did. I guess the explanation is that my car sits lower and/or I drive it too hard. I must admit that driving "normally", there was no rub at all. I'll try to post detailed pictures of where it rubbed.
Cheers.