There is no such thing as an xx Volt stepper. The only spec that matters is winding current.
Cheap consumer stuff like floppy disk drives used motors with artificially high winding resistance so they could be run without a current limiting resistor or PWM circuit.
So, for your use, all you need to do is supply enough voltage for the driver chip to operate, and then you will see that higher voltages permit the motor to operate at higher speeds before the torque falls off.
Berger-Lahr invented the 5-phase stepper, and licensed the technology to Oriental Motor, with theur Vexta and super Vexta lines of motors and drivers.
Jon