I run 18" wheels on my e92 M3s. The majority of forum members that track their cars run 18" wheels due to the greater number of track tire options. Personally, I prefer the look of the e92 M3 with 18" wheels!
I'm running a staggered 9.5/10 setup but I've seen people "functionally" run 10" (275/285 tire) F and 11" (295/305 tire) R wheels. Depending on the car, you may or my not get rubbing as you turn the wheels/tires on the F inner fender liner - appears to be a large manufacturing tolerance when it comes to fender liner placement!