Both of them are pretty close in HP gains. I would estimate h-pipe at 15-17 and x-pipe at 18-20.
The h-pipe makes it power down low. Inherently, it is also much louder down low. If you want a 60s muscle car sound, this is the way you should go. My friend has this one. Sounds badass, but is a bit too loud for me.
The x-pipe makes its power higher up as RPMs increase. It is pretty quiet at low rpms...So if you want to keep a low profile around town, go with this one. They don't get loud until you are at wide open throttle and that with when high pitch fury is released
. This is the one I am getting. Sounds more like an exotic car.
Both are pretty cool and you should be happy with either. Sound and where they make there power are they biggest difference between the two.
Thanks,
DoranW