I'm using 850W psu for 6 GTX 1060 without any problem. At my setting Power limit 80%, each card just draws about 95W.
Btw, I gonna build 1 more rig 6 GTX 1070 (each card might consumes about 145W), I'm not sure how much power mobo+riser uses, so is that ok if I use 1 PSU Great Wall 1250W?
Thanks!
If you are going to undervolt 1070 to 145W, then 1250W PSU is enough for your rig. Mobo usually utilize less than 100W, I have measured my mining rig, idle at around ~80W, riser will not draw much power, so don't worry about it.