http://www.linquist.net/motorsports/bmw/wheels
Scroll down to the table of results and see if anyone is running what you desire to run. I know on my personal car that 8.5 wide with +42 has me maxed at 255/35/18 all around. With certain models of tires and certain driving situations I have a bit of rubbing up inside the rear fender well, not at the lip.
I tried on a set of 17x9, +41 offset wearing 255/40/17 RA1s and didn't get 10 feet before the lip rubbing began in the rear.
What's interesting to me about the data in the table is, there are plenty of "no rubbing" people listing small offsets, wide rims, and even wider tires... yet there are equivalent spec'd cars further down in the red part of the table that do have rubbing.
I always make it a point to put context around the statistics, otherwise they're useless... like I have no rubbing with certain tires, and no rubbing on the freeway with a full tank of gas, but if I'm canyon carving with a full tank and junk in the trunk or people in the rear seat, major rubbing occurs. Most never comment on that and give a thumbs up for a +30 offset 19x9.5 running a 285 tire... in every f'n thread they participate in, and I just post "LOL" cuz I know from experience there's no freakin' way it works... in ALL situations.