Suggestion to the previous posting: There seems to be a lot of truism in statements like:
"" You can only save part of what is being wasted, or to put it another way, you can sometimes improve the operating efficiency of the motor by optimizing the voltage applied.""
Yes, this is true; especially, if a motor has a very high efficiency. Then, there is not much room left for energy savings, if that motor is properly applied and with an appropriate load, i.e. stable and continuous load.
Some room for energy savings may be left in switching from the rotary motion to the linear motion, e.g. from rotating machinery to linear motion machinery, if the mechanical application favors it. Then, the motor-load set efficiency is scrutinized.