It depends what you mean by best.  I am trottling back for best fuel economy.

I have set my MSI 5700 Mech to mine ETH at around 50MH/s.
Settings are as follows:
Core freq  1200
Mem freq   875
Core volt  731 mV    <- used Red Bios Editor to adjust from 800 to 725, but it wont go below 731
Power consumption reported by miner (Phoenixminr 4.9c) is 105Watts
GPU temp is 53 deg
Hot spot temp, which on my GPU is memory temp, is 82.
Fans are at 44%