Jeff,
I think what we are looking at here is an initially small but dynamic resonance within the stepper motor itself which results in the stepper motor stalling at a speed well below it’s maximum RPM capabilities. I don’t think anyone has worked out any formulae for calculating the mass of the damper or it’s distribution in fact I am not even convinced that anyone knows exactly how or why it works. It seems that all those dampers which have been constructed on the Zone are different or at least have a different mass distribution yet they all work. How can this be?
It would seem that the mass of a damper is not directly related to the stepper size but ‘trial and error’ is pretty much par for the course when designing one. I think you should give it a try and report back.

Tweakie.