do you have to get a muffler instead of a catback system?
A muffler isn't really about perfomance...but if you like that tin can look thats fine with me.
If you DO chose a catback system, the Apexi WorldSport is one of the best for the G3, as well as the DC Sports, Comptech Sport, Thermal Classic & or Stealth, and also the Greddy SP.