The only thing I've found that actually gives some noticeable increase in hashrate is to adjust the memory timings in the vbios.

I have the same problem as you with some RX580s. Unfortunately I can only use the 1750 timing there so they cap out at 27Mh/s with 2150 mem clock. But it makes no difference even at 2000 mem clock the hashrate is the same.

Grab polaris and modify the original vbios yourself, no reason to download random roms from the net.