Mucho gracias!
Here are my settings for my 570, I don't have any 580s, but it might be a good starting point for you. I'm getting 28+ mh/s @ ~80w per card.
Core - 1175
Mem - 1975
Core Undervolting - 850
Powerstage - 3
I have the same exact settings and its no way closer to 80 W per card.. 900 watts for 6 gpu rig (all 570. 3 diff models though)..