[BrianG]

yeah, many people don't realize that faster spinning motors are ok, as long as you are able to gear down enough, and some setups definitely are limited to how far you can go. It does take a bit of planning.

I would assume the most efficient operation would be the ESC going forwards since the timing would be optimized for best performance in that mode. Whether this means the motor is spinning one way or another is irrelevant.