[bojan]

Actually, with worm gear reduction, the main issue that will determine the required motor torque is the friction between worm and worm gear.
This friction will be highly variable, and is dependent (among other causes) on the pressure the worm teeth have to exercise on worm gear to achieve the required angular acceleration rate of the the scope/counterweight assembly.
As Andrew, mentioned, it could be surprisingly small at motor shaft.
But, this is not easy to calculate - so the experiment may be the only final judge here.

I have similar issue at the moment - recently I modified my eq 6 such that I have only timing belt with 12/60 reduction between motors (from old 5.25 floppy drive) and worm gears, and I am keen to find out how this arrangement performs with my Bartels motor driver. If the problem arises, I have the alternative ready: stepper with 0.48 Nm holding torque, nominal.