its prolly the psu guy, 1200w would barely be enough, I have an amd rig that does the same kinda with 6 gpus, windows ends up totally freezing up, considering the rig is really dependent on one thing! power
its not the PSU, I have a 6 card MSI GTX 1070 Gaming X 8G rig drawing 784 watts from the wall, using 1200w EVGA P2 PSU. nVidia cards don't draw as much power as AMD cards. I solo mine ETH. 182 M/H