I have had 18's, 19's, and 20's. Lots of folks running 18's which look best when running coil-overs. I personally like the track look of the 18's best. As far as sizing.... 10" in the front is the widest I would run and it will require significant negative camber (Nothing new to you judging by your picture). 12" is the widest I have seen anyone run in the rear but I wouldn't go wider than 11". I don't like the stretched look with tons of camber so I think 9.5" is perfect for the front.
'04 E46 M3 - Jet Black - Sold
'08 E90 M3 - Alpine White - Sold
'13 E92 M3 - Silverstone II - Sold
'13 E92 M3 - Alpine White - Ohlins TTX, Fall-Line Suspension Arms/Bushings, AP Racing BBK, GTS Aero, Cobra Seats, Akrapovic Evo, BBS E88