I have a 2011 Unltra Classic and I am added the Vance and Hines Power Dual X pipe and changing the Cam to a 255 Cam as suggested by Harley service for more horsepower. My question is regarding the slip ons I have been told by some to stick to 3 0r 3 1/2 slip ons and then the sales rep who sold me the bike new said if I am doing the stage 1 download and have the Power Dual 4 inch will be fine I like the Monster Round and Twin Slash cut. The Xpipe eliminated the cat. I am looking for more performance and looks and a deeper louder sound. The friend that suggested 3 or 3 1/2 said 4 and up will give me a lot of popping?