Dude.. Where in the heck did you find an RX580? lol. Vega from what I have been told by my AMD source (sorry, not Jim.. lol).. mid-LATE July.
but yea, I am running a 780Ti and it would seem.. Nvidia's cards can't do DX12 worth ****. I run DX11 mode, and its smooth as butter. DX12.. stutters and screen freezes galore.
Frankly, Nvidia just can't do DX12. (and I even tried bumping my clocks back up to 5.2Ghz just to see if I was CPU bound) and no change other than total CPU usage dropped to mid 50% from 65-70%.
780Ti clocks- 1,315Mhz core, 1815Mhz VRAM, GPU usage on maps like Amiens on BF1 (64 player, ultra settings, 1080p) 60-80%. Rarely ever see 100%. VRAM is pegged.