I went with the X-pipe for a short time. Part of the reason I went back to the stock muffler was easier communication with the passenger (s), ability to not only feel but hear the tire squeal; knowing when they were about to break loose cornering; and I enjoy the whine of the stock supercharger. I have no db results, but the stock sound is in this short clip:
http://www.youtube.com/watch?v=ao4XWu2hTBA
Aside from the lessening of weight, which is substantial, but which also must be accounted for from a handling perspective, I don't believe the gains are impressive: but then again, at times, louder is sweeter.
And, you do get a better "fireball" out the back end without the stock muffler; though you still get the fireball from time to time remaining stock, or so I have been told.
Pete S.