Yeah i think that the header's should not affect the overall rasp of your exhaust. It all depends on the cat-back you have. I beleive the main influences are the cat, as you suggested, and the resonators/mufflers your running. IIRC it's mainly the resonator though. Someone correct me if i'm wrong. Overall headers would be a nice mod, i think they give around 10-15 hp and would sound SWEET even with stock SVT exhaust. If you wanted it louder you could also look into an aftermarket cat-back system (but many will create rasp).
