Theoretically, yes should be more energy efficient as memory doesn't effect hash rate. My 1080s are in the high 2300s. What temps are yours running at?
Yea sry noticed that now :p
But I still get the same speed, even if I go -500 or +800 on memory clock. I still get around 2300 kH/s with ccminer.
Or is it more energy efficient to go with -500, is that why you said it?