Thanks everyone! I have heard the quicksilver and it sounds great, would be a good choice for the 04/05 models. To the best of my knowledge, the OC and SP exhausts make a little extra power. Also, Reiter has an exhaust system with a bypass valve, just like the OEM setup, but imo it is over engineered and overweight. The OC county unit costs around 4k give or take.
An extra benifit of the OC is a big weight savings, 50 lbs off the back end of the car if you combine the exhaust with a cat delete!