JT,
None of us have an absolute rule of thumb about calculating the actual VMCA for certain conditions, what we need is a sound understanding of the effect of aircraft systems, hence the reason this question needs to be explained to Tempo, by as many people as possible.
Q. what effect would landing gear extension have on the VMCA ?., also a fair question.
In the VMCA demonstration it will be seen that the aircraft will lose directional control both above and below the published VMCA, why would that be do you think ?.
what is the aircrafts actual all up weight, enviromentals, C of G etc etc.
the published VMCA is calculated in the absolute worst of both physical and enviromental conditions.
Agreed that it is something that you should not be anywhere near, but it is certainly in practice not an actual calculated and accurate speed, it's an indication of the absolute worst case scenario.
VMCA \ VYSE both these speeds are effected by a number of other parameters, again understanding the relationships is essential.
Arm out the window, Run out of opposite Aileron ?.