I have 4x Powercolor RX570 4GB with Hynix memory. Here is my modded BIOS with custom memtimings, and lower voltage straps, which can give ~30MH/s@1119/2080 -76mV
https://drive.google.com/file/d/14VxNiIvoFQVRgnILhBwQU9lzTW6Dh3cM/view?usp=sharing