Hi!
I am using this stepper motor
with this driver
and using this arduino code,
I wish to know the maximum rpm so I can rotate it as fast as possible, but not break the motor and driver.
// set the speed at 60 rpm:
myStepper.setSpeed(???);
could you help me?
There is no simple answer to your question. You will need to experiment.
As long as you have the current limit on your driver set correctly to protect the motor and as long as you don't exceed the maximum voltage specified for the driver (32v from what I can see) you won't do any damage. Within that limit a higher voltage should give a higher speed. You can get stepper drivers that will work with much higher voltages.
You can run into problems with resonance where the motor gets stuck at some mechanical frequency - especially if it has no damping load. Using microesteps might help.
I believe people have had high step rates with simple modifications to this Simple Stepper Code. It might be useful for testing because it is so simple.
...R
Stepper Motor Basics
oniudranij:
I wish to know the maximum rpm so I can rotate it as fast as possible, but not break the motor and driver.
Ah the regular "How long is a piece of string" question 
Possibly the max rpm can be calculated from first principles, but without knowing the load it is impossible. (I assume you want to actually move something with the motor).
The max running speed and max starting speed are two different things. To get higher speeds you almost certainly need to apply a speed ramp.
If you've got the equipment, why not just try it?
This is something to measure with the mechanical load attached. You'll need to ramp up speed,
such as with AccelStepper library, in order to avoid stalling when going from stationary to full speed.
There are literally half a dozen variables affecting top speed of a stepper, its far far more complex
than analyzing a DC motor, for instance. Resonance is a big issue with steppers.