Well if you are looking for more radical kits try www.ztrix.com. They have a GTO style convertible as well as racing fenders that are quite wide. Take a look at the Subtle Z kit. It preserves much of the Z's lines but allows wider wheels.

www.zspecialties.com

they have some great options

I'm not sure what tire size I need, but we would like pretty wide wheels (10") Right now, without the turbo on the car, it peels out in 1st, 2nd and 3rd. So I'd like something that is wider and stickier.