[svede1212]

I found a wheel/tire fit calculator. I am looking for the best width (I am steering towards a 9.5") and offset to accomodate my new 275/35/18 tires for the rear.
Here is the website:
Custom rims, wheel tire packages for your ride - RIMSnTIRES.com

2004 GTO 6 speed.

for 9.5" you'd need roughly a 48-50mm offset