I've got a powercore with the powerbomb header, my riding buddy has the Q4. Riding them & listening to them side by side, you can't hear any difference, nor feel any power difference. If i were buying a new one, & both were same price, i'd go for the q4 for psychological reasons. I noticed the most increase in power with the pipe. All the other performance mods are very minor & hard to notice, but i'm sure add up to more power. You'd have to measure the sound with a decibel meter to tell any difference. There might even be some.. should be, since the q4 is supposed to be quieter.