I started off by gutting my cat (no animals were hurt or injured in this process
)....and adding a "race" B&B dual out exhaust....I constantly get positive responses regarding the sound....however, the performance appeared to be the same....I recently added a Steve Wong chip, and as Tcannon88 mentioned above, the overall performance is much improved! My Carerra now pulls better in a more linear fashion...not just from 4000 grand and above....and appears to drive a lot smother through the rpm's (maybe it's just my imagination)....either way, it's a joy to drive more now than before and I never want to get out of the car!
Anywho, that's my 2 cents worth...good luck!