Why when mining monero rx480 hashes much better with 900h and rx580 hashes with 750h? Same setting and modded bioses and on etherium 580 is doing 30.5mgh and 480 is 29.5? What is going on?

I have some of ASUS ROG STRIX RX580 8GB OC with Hynix H5GQ8H24MJ, but hashrate is terrible low 28-29
and unstable. Any ideas for good mode?

I have noticed that overclocking memory to as fast as the card is stable doesn't necessarily produce more accepted solutions with the higher hash rates.  Does anyone have a benchmark of an average number of blocks found per/hr for a RX570.