Dr. Joe -
I am not understanding your use of gearbox efficiencies at the motor stall point. Gear efficiency is a function of kinetic friction. But, if the gears are not moving - the definition of stall, yes? - then there is zero kinetic friction. The efficiency should be 1.0?
But, if you are referring to electrical efficiency, then it is zero at stall, because there is no mechanical output - yes? That would not generate any useful equations, though, would it?
Or, are you simply putting the efficiencies into the equations at that point so they will propagate through the rest of the equations derived from it?
You are absolutely correct about this topic deserving a "white paper". It would be fascinating and useful information. But first I think we will need a thorough discussion of the basics of motor testing, and the four graphs - torque vs speed, torque vs current, torque vs power, and torque vs efficiency.
There is some good information on this site :
http://www.micromo.com/03application_notes.asp
See what you think of it - might be a good starting point. Of course, I am a mechanical engineer, so maybe this looks better to me than it will to you.