Widest rims I can run?

I work at a tire place and I can get tires wicked cheap....50% off all Michelines, Uniroyals, and Pirellis...and 10% over cost on everything else. Plus, I can get rims 10% over wholesale also..

I'm running stock Pony wheels right now, but I want to buy some Weld draglights. What I'm mainly concerned with, is what's the largest rim I can run in the rear? I'm thinking something like a 15x9 or a 15x10 would probably be sufficient. I'm hoping for at least a 275 tire. Right now, my 16x7's will only really fit 245's. I can run 255's, but they're too wide for the rim and it messes up the tire's footprint. I don't need the extra traction yet, due to my transmission, but I will soon when I replace it....and I'm tired of seeing 2.xx 60's at the drag strip.

I've got a 91 GT hatch...none of that quad shock crap.

Thanks

So if I don't want to modify the fenders or anything, I should run a set of 15x10's in the rear? Sounds good to me....