2175 MHz memory overclock is very high for a Bios modded RX 570 4GB card, which have slower memory than 8GB cards. My Sapphire Nitro+ RX 570 4GB card has Hynix memory and I can only overclock it to 2020 MHz before it starts producing tons of memory errors. It also depends on how aggressive the Bios mod timings are.
17 of RX 570 Sapphire pulse 4GB OC with Hynix Memory was running perfectly at 1150/2175 and that is the max limit a Hynix memory does. Only 18th cards started behaving not well and crashing several times.
Still the new settings are running from several hours without problem, I guess I will pay more electricity with 1284/2100 compared to 1150/2175 as the hashrate is bigger with 1284/2100