I have the staggered setup also - 17x7.5 and 17x8.5
I ran the OEM setup of 225 in front and 245 in rears when I had my old set. But I wasnt lowered so I had no problems back then. I'm sure I can fit 245, theres a lil more room before the wheel touches fender.
Heres mine, 1992 325i blk/blk with 168k miles! Still runs beautifully, i tracked it in November and it kicked ass!