I have the GT30R hybrid like pixel8r, and its fine, Nismoid doesnt know what hes talking about, because he hasnt driven a car with one inside it. I say unless you have the turbo or have expereince and degrees in turbo dynamics and physics, then dont explain it.
I even added a front mount recently and boost has not been any noticeably laggier. and im only getting about 260km out of a tank, so after an ECU next thursday, it will be doing MUCH better.
The fact that he has a power fc before a turbo upgrade is a great start, and I think that changing his manifold, getting a GT3076R, an external gate setup, he would benefit and that is that. If he wants to spend the extra grand or whatever, then get the HKS brand name turbo, but Garrett in itself are well above average, and leaders in their own right.