Well, I'll back RoxRocket up on at least once claim, and that's the fact that the cardoc exhaust setup is THE best sounding exhaust system I've ever heard in person on a 2.5L Duratec.
Mangler has it on his car, and it really is tha bomb! Whenever I hear it, I am enormously jealous.
As far as gains go, I can't really quantify them, but it sure helped his ride out, and it is definitely better than stock. You can't go wrong with a single 2.5" in and dual 2" outs to the back.
-Jeff -"The Crazy Canuck!!" -"Rice": Anything that looks faster than it really is...