the shorter they are the louder they will be. I had a set on w/ converters and they really are not very loud I think I had the 12" . No cats is another story.
I had the 3" Bullets bolted directly to my headers, loud as hell, sounds real good. Like a 5.0 should sound, don't know what length they were though. I am about to put 2 1/2" Bullets back on it but from the h-pipe, not directly from the header.