do a search on here for cat back and exhaust, and I'm sure you'll find a whole lot of info on this.
i've got a Borla catback, and a stainless hi-flow carsound cat, and love it. (if i were to do it over, i MAY have gone with a hooker aero-chamber muffler....but i LOVE all the nice stainless that is the borla system.)
the cat-back exhaust and cone air filter w/ tube were two of the BEST mods ive done to date. ($/performance)
my $.02
CaptTrev