I just seen a nice vid on youtube of a mustang with a x-pipe & then a h-pipe.. The h-pipe has a deeper growl to it for sure but the x-pipe does sound very good as well.. hard decision... ehhhh ... The x-pipe has better gas exhaust share as the H pipe shape at high RPM is almost like straight pipe.
Mustang Exhaust - H VS X Pipe - YouTube
Magnaflow & H pipe vs Flowmaster & X pipe on cammed mustang - YouTube