Typically a stock T5 car had around a 2.73-3.27 gear, 3.55-3.73 works well, but gear selection is also best when cam, heads and engine powerband are taken into account. 3.73's with a turbo means no traction, 3.00 with a monster cam is a dog etc. TKO is a better way to go if you want power, even a T5z is flimsy by comparison, and if you race frequently the T5 prolly won't last long(not with the typical driver anyway)