Stay at 480V, that is your nominal supply system voltage, you have no choice.
You will not find a standard 480V motor. You will not find a standard 600->460V transformer nor even a 480->460V one.
460V motors are designed and intended to be used on nominal supply systems of 480V +/- 10% (528 to 432). You do not need to make any accommodations unless you are outside of this range at the motor terminals. All of the motor performance information, including full load current, are based on a nominal supply voltage of 480V.
Look around, I am sure you do not have 600->575V transformers to feed all of the motors in your plant.
