Do you realy think an inlet manifold would have an overriding impact on Hp production???

The manifold would have little effect on where this engine makes power.
The torque line on any dyno graph is a representation of engine volumetric efficiency(VE). On a turbo engine, boost is usually the thing that has the biggest impact on the torque curve.

Hp is a function of torque and rpm.

The first rapid climb in the curve is where the boost is rising to 160kpa(already said this on an earlier post). once the wastegate is open the curve more closely follows the cam, headwork and manifold choices. The rise right at the top end is because of a little boost creep.
I built this inlet manifold for a road car with a mild cam. The length was to help a little either side of where the mild cam worked best, just to help flatten the curve. I just used it on this engine so i didnt have to make another one.
It would be different to what it is, if it was built for this engine.