I just put in a 2.5" Flowmaster 50 Delta muffler today to complement the S/C. It sounds phenomenal in a parking lot while jabbing the gas - a snorty bark of an exhaust note! It sounds like it should not be messed with. But it's really, really loud at full throttle, and still pretty loud inside just while cruising. I'm really hoping it will tone down a bit as it ages, otherwise I'm going to have to do some experimentation with other mufflers. At least they are relatively cheap

Anyway, I didn't go hog-wild with stainless steel like Cyrk did - I had them do all 2.5" welded piping from where the pipes from the cats merge together back to the muffler, up and over the rear suspension, then into a fancy-pantsy chrome tip. It should open up the exhaust enough for the engine to take a little more advantage of the supercharger.