Turbo talk

[Kreator]

So yeah, i was talking to a friend of mine, and we kinda wondered in this direction and this is what we got stuck on:

Ok, i'm gonna make assumptions so bare with me...
Suppose 2 KA engines:

        One is stock:       The other is modded:
HP:    155 @ 5600             180 @ 6200
TQ:    160 @ 4400             140 @ 5000

Those are hypothetical numbers. Assume it's possible to mod KA that way.
Now imagine a very large turbo (say t76) which spins up to full boost at 5500rpm on the stock KA. So basicly the stock ka can't use any of the goodness provided by the turbo, since say to keep in the power band u gotta shift at 6000. Now the modded engine has a smoother curve and teh power band is a bit later in the rpms range.

The question now is, will the modded KA benefit from turbo more than the stock ka? Or because of the modifications and the torque drop it will now spin up turbo at later rpms thus eliminating the theoretical benefits? In our discussion we settled that hp and torque shouldn't matter since the only thing that spins the turbo is the exhaust gas (amount and velocity) which are directly derived from the rpms. Is that theory correct or there's something we are forgetting about?