I was not able to run 6 cards ( rx480 ) with windows 7 at all . 4 was running ok , 5 had some stability issue , 6 never worked ... Tried everything Switched to win 10 , everything working fine . Installed WIN 10 ( disabled all updates , all automatic downloads ) , Intel Inf Utility , and rx 480 driver . With default settings all card hashing with 24.7 MH/s taking 1100 watts at wall ( 120 V ) , Then i "underclocked" my cards ( power limit , gpu speed - voltage , mem voltage ) ,    power usage at the wall become around 750Watts without pushing the default mem clock higher , with the same 24.7 Mh/s . Saved 350Watts per rig around 700watts ( with my 2 setup in the same frame) Used wattman for underclocking .