When I've run 17's they're as follows:
17x8 (4.75" b/s) 245/45's
17x9.5 (5.5" b/s) 285/40's
These fit my particular car no problem.I even shimmed the rears outward to give me extra inside clearance and I still had room to the fenderlip.
I would suggest running a 275/40 rear tire however,that will afford you extra room.Keep in mind my car's kinda a freak...
I currently run an 18" setup as follows:
18x8 (4.875" b/s) 245/40's
18x10 (5.625" b/s) 275/40's
You'll need to be spot-on to run this combination w/o issues and your suspension has to be quite firm.