James I would get HWINFO and take a look at the memory errors you are getting on your cards and reduce the overclock on the memory or increase the mv to 900 until the errors are reduced. I had one card that had a lot of memory errors I simply adjusted till I found they had gone then reflashed bios fixing to those settings.
I have a 12 card setup, but the rx570's pull 750w 167H/s ETH so your 1000w seems high. Mine are running 1075 1965 which I settled on for wattage.