perfromance wise they are absolutly identical... if you live in high altitude about sealevel the TT-S drives circles around the 370Z ... turbo vs n/a at high altitude is always a easy win for the turbo powered car..
straightline the TT-S is little bit faster with a slightly better 1/4mile time at a higher trap speed... at the track the 370Z is a little bit faster but needs a much more skilled hand.. and you have to be carefull about oil/water temperature and brakes
one thing to think about..the 370Z has dangerous brakes.. they work very well till they completely fail... C&D crashed a Nismo 370Z during their lightning lap at Vrginia International raceway at 130mph because the brakes failed completely from one turn to the next.. the laptime on this bumpy up and down track was much worse than that of the TT-S which C&D claimed to be one of the easyest cars ever to drive very fast.
in the Z, with no warning, the brakes went from fully effective to missing in action in a single, disastrous stop from 130 mph. The pedal collapsed to the floor, and what remained of the braking power was only able to slow the car at a rate very much like stopping on snow. Fortunately, no one was injured when the brakeless missile introduced itself to a retaining wall
I like both cars if you don´t race them regualry it is only a question of personal taste... the TT-S is easyer and cheaper to mod thanks to the turbo engine, the 370Z is meaner looking with no hairdresser image...