Has anyone used the Full Spectrum line of 4inch exhausts?. I want to upgrade mine but would like some input...ie....catback.....turbo back.....differences? opinions?.....any and all ideas/opinions welcomed and much appreciated for this PSD newbie. Just looking to upgrade to a tuner ( no racing tunes or anything crazy....just towing/mpg tunes)....all stock exhaust....and damm the EPA I'm killing the cat ( but will save it JUST IN CASE)