(Discussion)Most effient voltage??

Has anyone spent the time to figure out the most efficent voltage for a given motor??

Take the the most popular motor for example.
The BK 7 or 8 XL series.

I cant find the amp ratings or the KT (torque ratings). Please post a link, if you have one to the motor specs.

I am an electrican by trade and still have a hard time figuring out all the variables.

As voltage increase so does efficenty (spelling??). So we need to discover the best voltage for each given motor.

Being I have an 8xl I would like to figure out the best voltage.