Since this is for a CNC machine all of the speeds will be controled by the Gcode from the CNC software.I would say you need about 25 discrete velocities that you can use to accelerate, run and decelerate.
Isn't that the defination of a pulse train? Not trying to argue but to understand, with a stepper driver the pulses come from a 555 timer type circuit, usually unless it for a CNC.timer based state machine, each time the timer expired,