I think 17s are too small for the non-Brembo GTs. The Mustang is supposedly moving to STU in '14 so you may want to wait a bit so you can see who your competition might be. I'm waiting to see what they do with the PAX as well.

 

I'm in SM because of my LCA relocation brackets and bumpsteer kit. Oddly enough, my watts link alone wouldn't have forced me into that class...

Seat time is your best mod if you're just starting out.