Running 2 rigs (soon to be 4 rigs) with 4 7850s each.
Each GPU gets 320 M/hash at 1095 OC. For a 24/7 operation I cant get them to go higher. Also its open air non cased, in front of a window AC unit.....
7850's are the best bang for buck, unless you can get 7950's on sale.
what's the PSU your are using to power up these 4 together.
BTW which 7850 still have undervolt feature available or are they all locked now?