The biggest combination I've fitted to my unaltered rear suspension setup is a 255/45/17 on a 17x8 with 5.25" of back space. I don't see it being possible to go with any wider then an 8" rim without doing some other modifications to the car or suspension.
For the front wheel and tire specs 7" wide rims are the max you can go with an all stock font suspension setup. This is also true for CBR and CPP bolt on mini subframe kits. The back spacing is an extremely critical dimension to getting a big diameter 7" wide rim to fit. Front wheel back spacing will need to be 4.5-4.75" on a 7"' wide rim to clear the fender and suspension up front.