Stuart,
You will find basic info on the Gecko Drive site. No use me repeating it here.
How much torque do you need? Calculators by many of the motor manufactures are based on a number of assumptions and thus they are subjective and get you in the ball park. Sizing is not straight forward since a few things come into play that are not calculated....like:
1.Torque to just move the axis ( this can be more than one thinks on a tight system)
2. Acceleration not only from start but when doing 3D cutting since it becomes important
3. Torque required at the feedrate and material being removed, which can be calculated / estimated for metal but I have never seen anything for differeNt kinds of wood.
Note that power ( speed x torque ) is what your after.
So be conservative on the torque requirements since the cost is not that much more for the motor, but, do make note that all of the sizing is a comprimise and rationalization of desired operating conditions.
RICH