Using Wattman, your values may have to be tweaked depending on the silicone lottery:
Memory: 2200mhz (overclocked), 975mv (underclocked) Power Limit: +15%
This will draw 825w from the wall with 3 cards.
Stock for these cards are:
Memory: 2000mhz, 1000mv Power Limit: 0
In the Claymore Miner config.txt:
-ethi 8 -dcri 60
I left the Core clock at stock which is defaulted to 1266 or 1288 (XFX version)
More can be done with tweaking the Core Clock, but my 850w power supply was already at 825w with 3 cards and motherboard/fans.
Installing another power supply for 3 more cards will let me tweak the numbers some more.
With the settings above, I was able to get:
ETH/ETC: 27 Mh/s (26 Mh/s on one of the cards) DCR: 810 Mh/s (790 Mh/s on one of the cards)
Heat and Fans:
Max: 80 C Target: 75 C