The X is better than the H, along with the 2 1/2" pipe. Both would help. The mufflers can be decieving. Big body with big inlets and outlets somtimes does not = big flow. I would look at the mufflers that ths F.A.S.T. guys are using as they are in 10's and 11's at the strip with a 2 1/2" exhaust. I looked at your engine specs and I believe some head work as in a nice port and valve job would be where I would put my money after the exhaust. Hope you find some of this useful.