X or H is whatever your sound preference is. X is more raspy than an H. Ppl will try to tell you one is better than the other, its a pointless argument. If there is a power difference, its so minimal as not to be worth it.
I personally hate Flowmasters, if you've ever driven an extended time with them on the highway and an OR pipe or a pipe with high-flow cats you'll understand. The drone is so bad its not even funny.
2000 Mustang GT Steeda #0048
Just because I give you advice, doesn't mean I know more than you. Its just means I've done more stupid ****.