I'm running 235/45-17s BFGoodrich KDWS on a 7.5" wheel (2004 STi) and have no problems with rubbing. I'd say an 8" wheel is "ideal" but 7.5" is okay. This is my rallycross setup so they get worked hard.

 

I just recently went from a 225/45-17 S0-3 to a 235/45-17 S0-3 on a 7.5 inch rim and haven't had any problems at all. It does feel just a tiny bit "slower" when i begin to accelerate but there's not a major difference. This is a pic of my front wheel. Stock struts w/ Whiteline Flat-Out springs.