Swapping the Head pipe is a must, at the very least do a search on the site for gutting your CAT, on the bike not fluffy, and go through that process. I am switching to the Fullsac X pipe for two reasons. 1: Doesn't matter as much what I do with the slip-ons since the back pressure is managed by the restriction in the X pipe. You might swap out a couple ft/lb for HP but not enough to really matter in my opinion. 2: Oddly enough it just sounds a little better than the gutted CAT, I listened to both of them and liked the X pipe better. The extra couple of horsepower was not really the incentive, I just can't imagine a situation on this bike where a few more ponies would make a difference. In theory the X-Pipe would run cooler since it is ceramic coated, but that is just a theory.