Buy a new exhaust system fo sho!
Those guys are nuts! You should keep your stock one stock and save it for just in case you don't like the aftermarket one or when you decide to sell the car.
F.I. and Berk are on the top of my list. You should check them out. I just don't see modifying the OE exhaust with an X pipe for 600 bucks. You won't gain that much more horses with it.
Good luck with your desicision!
