Do you guys only lowering the TDP for optimal efficiency? Or do you actually change the voltage? If so, how?

My settings now are:

TDP: 75%

Core: +130

Memory: +100

Fan speed: 70
Temperature is between 55-65 for 3 cards mining ZEC, 730-750 sol.

Not sure how to messaure the watt usage since the miner I use don't show it.