Own a 15 turbo, trade for GT3??
 

I assume you are referring to the Cobb tune

Speed 21, what exhaust are you recommending?

I'd go with Europipe, Sharkwerks, or GMG. All good. SW is best bang for buck.
Mine is stock by the way - it's my DD.

Akra or Cargraphics.

Capristo if you want your TTS to sound like a video game. Space Invaders, to be exact.

Viper, Europipe....clearly the best catted system for the car by a country mile. Anyone in disagreement please correct me if you can find a better cat being used. EP is also the only one providing emissions data and back-pressure reduction data in comparison to stock system. Anyway if it doesn't cure the cars ill's nothing will.

Assuming you've become accustomed to the superiority of TT's power (out of the Porsche line -up), I too can't see a GT3 fixing your itch for long and concur with others making the comment you will likely tire of GT3's ride as a daily if street is the use. The 3 is more in its own on the track than the street. That said the TTs will also give the 3 major grief on the track as well. So, anything less (on either) IS a substitute IMO!

Outside of the Porsche playing field, the 488 appears a definite solution too. :D

I'm a big Akra fan as well, great quality, but aside from being very costly they quote CEL issues if the car isn't tuned. Not sure why they haven't come to grips with that yet?? Heard it was also an issue on the 997tt too. Cargraphics and Crapisto would not be options for me personally, purely due to cat design, and Capristos potential valve failure issues. I'm big on performance and reliability... Sound is always subjective but (for me) it's nice to have the sound matching the badge on the car and not some attempt to sound like some other exotic.