Soon enough you will get more GPUs, and should take that into consideration, i.e. I would suggest to get PSU which will be able handle 6x GPU. I am currently running 7x 1060 3gb with 750W PSU. Because I am using powerlimit of 75W for each of the cards the PSU is able to handle it. But:
1. the set up is not definately recommended due to lack of risk marginals
2. I need to powerlimit the GPUs, even if I could gain more with no powerlimit

morale of the story: Don't go cheap with PSU

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Tigel