And single tips are slightly quieter than the dual tips, and H pipe is slightly quieter than X pipe. Greg also told me the hp difference between the resonated and non-resonated exhausts is minimal, and nothing you would notice.
He told me the non-resonated versions are for the heavy duty drag racers who want to gain every bit of hp from any place they can to get the highest hp possible. He recommended the resonators for a street driven car if you had any concern about the sound level.