You'll get mixed opinion's on difference's between the X & H Pipe's. In Most circumstance's an X Pipe will make more power then an H will, and the exhaust tone is defenitly the most notable difference. From my own personal experinence I've found the H to have a more deeper sound, and the X to have a more Raspy, Nascar NC type sound to it.... it really depend's what style of muffler's your using as well. I've found that chambered muffler's (Flowmaster) don't sound as great behind an X-Pipe, but that's my opinion. I'm running Dynomax Bullet's behind my 408 with an X-Pipe and it's the grestest sounding car in my area. Nice and deep at lower RPM's, and loud/raspy as hell when you get into higher RPM's.
I've got 40 series flowmasters on the car, I think theyre 2 chambered. I was just thinkin maybe it was time for a different sound. But I dont think I want to go changing the mufflers just yet.