The concept used with these drives is based on current drive not voltage . The high supply voltage is used to overcome inductance and force the current to rated value as fast as possible resulting in maximized torque. The current sensing sets the current cut off which in turn holds the winding voltages to sane values.
As previously stated what is desired is maximum torque over a very broad speed range. Unfortunatly that speed range usually includes the resonant speed of the mechanical elements as well as the electrical resonance which is a product of the motors internal characteristics and the output circuitry of the driver selected.

A properly designed system will preform very well producing good torque with relatively low heating in the motor or driver until it is operated in the resonance area. It then becomes a totaly different thing about on the same level as a teenager after that magic visit from the Knowledge fairy.
A second reference on steppers is
New Japan Radio who bought out Ericson's industrial control division. They had all of the app notes from the Ericson "Industrial Circuits Data Book And Stepper Motor Control Handbook" on a site IIRC after the buyout. I have the book and if it can be found it is a gold mine Terry