First of all, torque times RPM is equal to power (times some arbitrary constant). If you´d have a low current high voltage generator, then yes the torque would be lower, but the RPM would be higher to get the higher voltage, and you gain nothing.
Or in other terms, low or high voltage does not matter, as the efficiency of the generator is basically the same. There is no power inherently lost by using low or high voltage, and unless you exactly quantify the losses, the two are exactly the same.