Sapphire RX 570 NITRO 4GB Hynix
XFX RX 570 4GB Elpida

Stock settings and BIOS I get 23.x Mh/s on ETH only and 21.x/640ish ETH/SC.  I've tried Anorak's BIOSes as well as setting the straps through Polaris and OCing using Wattman and at least 3 different AMD drivers.  Nothing works, I see no change at all.  I am running out of ideas.  Tomorrow I will move one of the cards to another computer just to see what happens.  If I'm doing something wrong I have no idea what it could be.