The power difference between the two is pretty minimal and the h will put out a tad more low end torque while the x will give more upper RPM power. I would make the choice based on sound preference. The H gives a lower muscle-car type sound while the x is more raspy.
you might want to get a little better brand than mac. there products are known to rust because there not stainless, but they do sound good. MRT has stainless ones but they are pricey. i'm in the same boat as you but i think i'm gonna go with the slp catted x.