The rotors on a GM-4 and GM-8 are identical. The only difference is a slightly better compressor housing and a slightly better exhaust elbow. The waste gate was moved out of the exhaust housing into the elbow on the 8's and I've been told that the elbow is more efficient. With that said, I don't think you'll see significant performance differences between the two. The wastegate move was to improve reliability of the bushing (mine failed) and had nothing to do with performance.

I have an outline map of a the GM series compressors...it has no detail and IHI will not even respond to my inquiries. The other manufacturers have been very responsive to my questions.

It is fair to take my comments as being applied to the GM-X series in most cases.

My main comment here was to clarify the relationship between peak torque and peak power and to give you some of the rationale behind choosing shift points. The turbo talk was simply to help explain some of your observations.