So... After some testing...

My best settings for now:

GPUClock 1050
MemoryClock 2000
GPUVoltage 987


straps copied from 1750 to 2000

4 GPU Asus Strix RX 580 on Samsung memory - 111Mh/s (Ethereum only), 525W from wall

I'm very impressed by temperatures: about 50-55C

Can anyone share their best settings for that card? Maybe some bios mod?