G'day mate, Have a little bit of faith in your T5 (although the T56 is a worthwhile mod, don't get me wrong), if you find a real good tuner (which is like a needle in a haystack, I'll admit), a tuner can make your T5 work. It's the low-down torque which destroys them, if you've got a good tuner he'll be able to tune it to suit, APS have already proven this with their T5 gearbox running high 10s, its all in your tuner. I really wouldn't bother with the exhaust system, I'd look at putting in a high flow cat and more high flow mufflers. By all means, a good 2.5" cat back system would be good but to sum it up, the best investment you can make is a good tuner.