From my experience, H-pipe sounds a bit deeper and gives that rumble, X-pipe is more aggressive sounding and has more rasp to it. Though the end sound depends on your cats, muffler, headers, resonator, and even the material the exhaust system is made of. Also, supercharger makes it louder and turbo tends to slightly muffle it. But when it comes to the power, having cats and a muffler will make more of a difference than the shape of your pipes, X-pipes are slightly better at scavenging, but not enough to say its better.