Here's a dyno chart showing the difference between the 06 catalytic mufflers and the 07 stock mufflers as far as power on the same bike.

Blue run is cats, red run is 07 stock mufflers

http://i149.photobucket.com/albums/s45/bills985/catmufflercomparer.jpg

Interesting with out cats having a torque dip at mid rpm range!

its possibly were the bike is tested for EPA so it dips then picks back up.