I'm running 18x10 275s with a 6.6 back space on my DSE sub with C6 Z06 brakes. These wheels were ordered with a thick mount pad. Not sure if that helps you or not. But I can tell you that the 18x10 275s fit the fenders and inner wheel wells with no modifications.
__________________ Steve Hayes
"Dust Off"
68 Camaro
Speed has never killed anyone. Suddenly becoming stationary, that's what gets you! "Jeremy Clarkson"