Don't go cherry bombs or anything similar, you would prolly burn out the fiberglass packing in a hurry if the car is frequently raced. Personally, I would go with something stainless or aluminum anyways for corrosion resistance and longevity. Beyond that, I'm no help for sound opinions. But as someone mentioned, if your tracking the car and switching the exhaust for the street anyways, open headers with some tips out the back would seriously save some weight.