Originally Posted by annemarie1
I heard once that 220 volts at 60c/s is the best most efficient supply for motor loads

I'm not sure where you heard that, AnnMarie.
3 phase 400V motors certainly have advantages over their single phase counterparts, as in they are more efficient, quieter, are pretty much self-starting and draw less current for a given size of motor.
Of course, you do need to have a 3 phase supply to take advantage of this.