I have a 1000w PSU, only have 3 cards at the moment and waiting on riser but will go to a 6 cards if i can
For ETH ONLY 1000PSU should do fine but with dual mining it can not.
Optimized rig of 6 GPUs should take 800-850Watts from the wall but dual minigs increases consumption.
I have 1 rx 470 and 5 RX 570. Applied some mods. Not the most optimized rig of course:
168-169 Mh/s ETH-->850-880Watts
+2700 Mh/s SIA when dual mined--> 1020-1050 Mh/s.
I rather keep my PSUs comfortable instead of squeezing every bit of juice it has.
I prefer maximum %80 capacity of PSU on full load.