I have the Dynomax Super Turbo's on my car. It actually wasn't very loud at all. You want to make a REAL difference? Get an off-raod H/X pipe! WHen I got mine there was a 100% difference in the sound. It was louder and meaner, even with stock headers.
Even if you get a pipe with Cats, you'll be happy.
------------------
Driving: 1998 F-150
Far way in Edmonton==>
1995 Mustang GT