You should PM a guy in Houston named Ajax-Prime. He had an Eisenmann Race and then recently went to Eisenmann Sport, because the Race was too loud. Also watch our video here if you haven't yet:
http://www.m3post.com/forums/showthread.php?t=303733
If you like Eisenmann, then go with the Sport version, is what I'm sure Ajax-Prime would advise. The only quiet exhausts I would consider are Dinan, Remus Sport, and Eisenmann Sport.