I just changed my MAC o/r H for a UPR o/r X and I am much happier with the X pipe. Sounds great with my Dynomax super turbos, and I know most will flame me for this but it seems quicker using the Butt Dyno. To be fair though, the reason I ditched the H was because it was leaking bad and I have heard that an exhaust leak can effect performance. The other difference is exhaust note. The H will have a deeper rumble, the X is a little more quite and has a higher pitched raspy sound at full throttle.