Controlling Stepper Motors
The maximum rate you can move a stepper motor is based on the shaft torque and coil current.  Attempting to move too fast against too high a torque will cause the motor to become desynchronized with the step impulses and move unpredictably/uncontrollably.

Here's a generalized graph:



The whole curve shifts up and down with current.

Most drivers' speed will be orders of magnitude faster than any motor, the few exceptions are things with a bunch of protection/intelligence (of which the Darlington driver you linked has neither)