[full quack]

I agree with 1980 911 SC,
I too think the supercharger is under rated for your application. On V8 street supercharger applications, the blower is almost always running at 1/2 or 2/3 crank speed, NOT twice crank speed! That's for top fuel stuff.
A supercharger is a positive displacement air pump, so for every rotation, it pushes a set amount of air, period. The supercharger does not care what is down stream from flow, it simply pushes air at a given constant rate, at a linear progression of flow, with linear progression of rpm.
Therefore, it seems to me that if your engine is hitting a wall @ 3000rpm on boost & HP & torque, you have simply run out of air supply. Your AF ratios should still stay normal-ish since it is flow that your sensor plate is sensing.

But what the hell, I could be horribly mis-informed & delusional, but the statement from Hans, saying it is not uncommon to lose boost because of port flow, just does not sit well with my pea brain.

Mark