Well I've been doing a little research cause I've been thinking of getting a new set of rims myself. Stock GN wheels are 15x7 with 4" BS, TurboT alum wheels are 3.75" BS. My GN wheels with 275/50/15s on them rub slightly, so I'd go with a slightly smaller BS, such as 3.75 or maybe even 3.5. The TTII wheels come in 15x7 and 15x8. I think you can get "Custom" sizes at special order, such as 15x8.5 with 3.75 BS, or 16X8.5 whatever you want, but you have to wait 8 to 12 weeks for them and there will be no refund so be certain on the size you want.
Also, remember, the shorter the BS, the more the wheel will be moved out to the fender, so with 3.5" BS and 8.5" width, that means the wheels will be 2" closer to the fender than stock.