I am using AMD software version 18.3.4, you dont need to restart the vegas with this software version after each restart, it will auto detect. There is no special setting, I just had to reduce the OC on all cards, so running 900 on memory and 1300 on core. 950mV on core and 900mV on mem. 18kh/s, using SRBminer, tried cast too, same results. However, I have disabled the ADL reporting and I am using openhardwaremonitor to check temps and fan speed and I have also disabled the gpuwatchdog. That's it. Screens:

https://i.imgur.com/POSApjf.png