what tool are you using to adjust overclocks  and i am using sapphire nitro+ 570 4GB i am getting 29.6MH/sec @1100/2000. what changes do u made in bios(modded). try polaris bios editor 1.6.7 for the auto timing straps. when u click the one time straps it will change to the best timings.and also check voltage limts

polaris bios editor for windows (run as admin. user)


https://github.com/jaschaknack/PolarisBiosEditor/blob/master/PolarisBiosEditor.exe