Hi Ben, great choice to have to make.As the saying goes," one mans meat is anothers poison" , but here are my thoughts for your consideration. Both are fantastic cars, but totally different. The Gt3 is without doubt the more focused drivers & track day car, great sound, great for that weekend blast. BUT the VERY firm suspension & high noise levels make it very wearing as a daily car. If the car is for track days & weekend only this is a super choice, although I think that it shoul have PSM. BUT it' s not for me, having had two C2' s (one the new facelift)
I fell in love with the TT, it can be a comfortable mile eater, has all the toy' s (great stereo, PSM etc etc ) & is a simply great drivers car when you are in the mood.
I could not believe how much faster point to point it was than the C2' s, it' s the combination of the upgraded chassis, brakes & engine grunt !! Be assured the 996TT is as awsome as (all) the press say it is, probably the fastest point to point car on the planet. It' s biggest drawback is the grunt is addictive & you easily find yourself doing speed' s you shouldn' t...sorry officer. The GT3 may offer that little extra driver interaction, but the TT isn' t far behind & offers so much more besides, grip, go & grunt in all weathers or cruise home with all the bells & whistles !! Best of luck with your decision.