Why would u upgrade stock exhaust?- That is the most important question...
If u want it to perform well, dont bother buying a cat-back at the moment. Buy a header or pulleys or get an ECU reflash, anyone of them will make more difference performancewise than a cat-back, UNLESS it is a single outlet cat-back system, but those are loud and pricy, and it sounds like u want to avoid those. Even then u would only gain 10? HP. With a dual cat-back u gain... 0-3? 5? HP depending on the system that u pick.
Now, if u are looking for sportier sound... then yes, buy Apex'i WS2 or Comptech cat-back exhaust. They both are relatively quiet and make gentle sound. Sound is indeed way up there....
I hope it helped....
