I am looking for a new exhaust for my 07 KC and wanted to know your opinion on the Magnaflow Cat-back system. One thing I want to know is if I just put the 18" #12258 on my stock exhaust would I be getting the same kind of performance? Is it worth the extra to go with the full cat-back exhaust? Anyone using the full system right now? I can get it the full system for $450 now free shipping.