im actually wondering the same thing, i currently have an apexi N1 on the car with asp headers and no cat. The car is just way too loud to drive around my town and the surrounding towns without getting pulled over/drawing unwanted attention by the cops. In actuality, how much power would you be loosing on a ve with n1 cams, jwt tune and some other bolt ons. I honestly couldn't imagine more than 5-9hp.
I was checking out the VSR 2.5" exhaust since everyone is saying that they are great systems and the noise level is just right for a DD