i think its personal preferance. guys that like the x pipe say it flows better, and guys with the h pipe say its balanced better. ive never seen any proof say one is better then the other. its all about the sound. now, certain manufacutures will show the difference in their ccatted pipes and off road pipes, and i saw a mac dyno chart one time for the economy, off road, and prochamber, and the difference was not even noticable, if i remember correctly, 1 hp between each. you will never notice 1 hp unless your john force.