I have the same Powercolor Red Dragon cards with Hynix/Elpidia dual timings. On Windows 10 with the AMD blockchain drivers for ZEC I get ~315 H/s with a 1325 MHz core clock, 1950 MHz memory clock, -96 mV undervolt and -15% power limit in Afterburner v4.4.0 beta 19. The bios was modded with the Polaris Bios Editor v 1.62 'one click timing patch' from jaschaknack. If you can't undevolt the cards, remove the drivers in safe mode using DDU and try again after installing the blockchain drivers. If you have a bios mod, for RX 570's you also need to run the pixel patcher to bypass the driver signature check.
If the card crashes after it starts mining, try lowering the memory to 1900 MHz and the default 1250 Mhz core clock. For ZEC it shouldn't make that much difference.
