I have a hard time believing that the exhaust changing would have little effect. I think you're logging the wrong things if this is the case. You should be able to see a change in WGDC vs RPM. You're either raising exhaust pressure by opening the valve early or reducing it by opening late. There should be a direct relationship to spool vs RPM seen.
And modding for a single turbo is no different that twins. Mass is Mass and Inertia is Inertia. Two or one is irrelevant.
And modding for a single turbo is no different that twins. Mass is Mass and Inertia is Inertia. Two or one is irrelevant.