Use the following for a stable system.  I have 4 GTX-1080's and 4 RX-5xx running on one motherboard that can do 13 pice total.

[Power->Watts]
1380 -  1440

[Nvidia Windows, Device Manager]
23.21.13.9077

[Geforce Version, Nvidia]
390.77

[AMD Windows, Device Manager]
22.19.659.0

[AMD Setting->Software]
AMD Beta: 17.30.1029-170808a2-317304


[Hashrate]
220 - 350 Mh/s

PS: GTX's are far better per watt and there is where the improvements should be.