I don't have any Sapphire Nitro+ RX 580 4GB cards, but I know my Sapphire Nitro+ RX 580 8GB SE cards with a Samsung/Hynix dual memory Bios don't like a core clock over 1150 MHz. If I increase the core clock by more than that, the hash drops. I use the Polaris Bios Editor v1.6 from jaschaknack, 'one click timing patch' Bios mod with a 1150 MHz core clock, 2100-2200 MHz memory overclock, -15% power limit and -96mV undevolt and get 30+ MH/s ETH + 850 MH/s DCR dual mining with a -dcri 28 setting. You also need to use Afterburner v4.40 beta 16 or higher to be able to set the power limit and undervolt with the blockchain drivers.
https://github.com/jaschaknack/PolarisBiosEditorhttps://www.guru3d.com/news-story/download-msi-afterburner-4-4-beta-18.htmlAlso set your virtual memory on Windows to at least 16GB if you're using multiple GPU's.