I did one click straps (polaris bios editor 1.6.3), TDP 115, max power limig 120 for bios.
And then in miner i do -mclock 1950 -cclock 1150 -mvddc 950 -cvddc 950

I get stable 27.3 per card in 6 card rig (more than 3 days now without restart or anything) with a total of 800w from the wall. I could probably go lower with those voltages too, as ive seen some those with 900 for both voltages. Its quite decent

If i wanted to optimize even more i could as i managed to go over 28 on all except 1 card (main one whose riser goes in pcie16 slot and stalls opencl) with a bit higher memory(going -mclock 1950,1975,1975,1975,1975,1975 for example). But didnt want to bother.