Dual or single mining? For some reason on my 570 I'm getting about 25-26 MH/s either way, so I'm dual mining on mine (right now ETH & DCR) Getting 25.5/635 doing that. My 580's I get about 30.5 single and 28.5/450 (have to lower dual mining on the 580's... no clue why) dual.
All single mining (ETH)
My card is Sapphire RX570 8GB Samsung. Can get to 25, but not 26. Something is off with the straps.
Need to look into it.
When dual mining - gets me to 24.8/740 (ETH/DCR)
Which BIOS mod are you using?
Right now I'm using Anorak's for my 570 - I'm planning to do my own this weekend. Would be nice, but I doubt it, if I could squeeze another MH/s or two out of it.