for silence and best efficiency / miner lifetime (my personal preference)

Expected hashrate: 15Mh/s to 17 Mh/s
Expected power usage: 700 - 780 watt

set the frequency at "400mhz", set the voltage to "lowest". Now slowly increase the frequency until you see HW errors. When you have a few HW errors an hour you found the sweet spot
set the fan speed manual somewhere between 20 - 30 percent. Chip temp should be somewhere between 75 - 80 degrees max.