Maybe someone can answer this for me. I am looking to upgrade my exhaust to a 4" MBRP cat back exhaust system. I here everyone commenting on how the turbo spools up faster and it sounds cool. But my question is, do you get the same performance and audible effect when you have a cat-back system vs. strait from the turbo? Or do you loose a lot of the sound and performance because you still have somewhat of a restriction still (the Cat)? Also is there a big sound difference between the 4" and the 5" system? Any suggestions or comments please, I plan on doing this upgrade soon.