Since building my first rig last June, i've always had this rock-stable settings for six of my Asus Dual OC 580s 8GB Samsung memory

-cclock 1260
-mclock 2050
-cvddc 925mV
-mvddc 925mV

This yields me a constant 29.1 to 29.3 across all cards (175 total) and pulls about 1175 up to 1200w. High, I know but they go for weeks until needing a restart.

Earlier this week, I played with them again to squeeze in few more Mh. These are my settings:
-cclock 1140
-mclock 2075
-cvddc 875
-mvddc 875

They average a total of 177.5 now and cards hashes from 29.5 up to 30.0. But the best thing is they now only pull 1035w dual-mining with DCR.