Firstly -I have heard that steppers have there most torque when running very slowly?
Is this correct.
The torque is max at the slowest rpm of the stepper and degreases as the rpm increases. So yes, BUT,
you also want to have a decent axis resolution by micro stepping, adding gearing increases delivered torque.
Without any motor model / make you know nothing of that motor. You could mount it such that you turn the shaft and see max generated voltage.
Also can measure resistance, capacitance/ inductance of the windings. All a trade off of speed, torque, axis resolution.
Suggest you go to the Gecko Site as they have a lot of info on steppers to increase your understanding
RICH
BTW, Steppers are rather cheap these days and worth buying new and thus you know what to expect when installed.