When i first recieved my xfx gts, i was disappointed also with ALL of them.. but after a few tweaks they are doing better than of my other cards..
What mem type?
My XFX black core edition RX580 only does 21mhs with tweaks in Afterburner but without bios modding. When I tried to mod the bios, somehow the card got bricked, so I had to revert to the stock bios saved. I guess I should give it another shot.