Sorry, I realize this is a bit of an old thread, but hey, can't blame a guy for actually using the 'search' feature...
My main machine in this game is my dream car, the ST165, or 4th gen Celica AllTrac (listed in GT4 as the '86 Celica 2000GT-Four)... I tuned it how i'd want it in real life - close ratio, rally spec'd, and geared toward low-end torque rather than massive HP... as much as I'm a fan of superchargers over turbos, this unfortunately is not an option, so instead I bought a stage 1 turbo w/ the smaller sports intercooler on purpose, in favor of the non-existent lag. It's beautiful on technical city courses with uphill climbs like Citta di Aria, where the throttle is constantly feathered and much of the track is driven at less than 60mph.
My question - the Original Turbo, or stage 5, that the tuners offer, boasts big HP w/ no torque loss - has anyone tried it? can it handle technical courses and maintain low-speed torque?