Higher voltage give higher torque except for very slow stepping where there is no difference. That is assuming the same current. You choose as high voltage as you can afford, and a driver that can deliver the current your motor is rated for.
Your assumed motor will draw 1 A if you put 5V over it at standstill then it is DC current and the resistance of the windings are what counts. Use Ohm's law. As you start to move the motor you don't apply DC but AC. Then the inductance of the windings come to play. An inductance don't like changes in current and oppose that, so you have to apply a higher voltage to counteract this. So Ohm's law does not work any more as the current lags the voltage. Increase the speed and at some point the voltage you have available will not be enough to drive the 1A current through the motor. At that speed the current and thus torque starts to fall rapidly with further increasing speed.
You can use as high voltage as the motor insulation is designed for, a chopping drive will at all times chop the current in exactly large enough chunks that your 1A will flow. Until the speed is too high for the available voltage to give that current. Then the chopper will not be chopping anymore, but give all it have. It's the "throttle to the floor" condition. Compare voltage to HP and current to torque.
I have tried steppers with 70V drives, and they can reach far beyond the speed you normally think of with steppers. At these speeds they run almost as smooth as any other motor. No knacking or growling.