It really depends on how hard you want to push the card / what the extra power consumption is worth to you. I'm running:

-a 4
-h 1920
-cvddc 850
-mvddc 850
-cclock 1150
-mclock 2250

Average Hashrate for last 6 hours: 2,963.3 H/s (or ~493.9 H/s per card)

Runs about 80-85w/card and maxes out around 779w total from the wall (total rig - 6 RX580's, 1000wPSU + 850wPSU). Temp 45 (fan 60%),

I'm kinda curious what the flags are to get 700+ H/s though?!