An H-pipe will offer a more bassy, low rumble... like an old musclecar
An X-pipe will offer a higher-pitched sound... more like an exotic car sounds.
The difference in gains between the two is comparable with the H-pipe making a bit more low-end torque and the X-pipe making a bit more HP (due to the fact that exhaust gases can merge more easily in an X config.)... depends on the combination, really, but that is a generalization. From what I've been told, the Mac Prochamber is virtually the best of both worlds, as far as HP/TQ numbers are concerned.... and has it's own sound.
Check out
www.mustangexhaust.com if you'd like to hear some sound clips of various setups... I'm an X-pipe guy, I guess.
