wow, thank you so much for looking into things. I can't imagine why these stupid Vega cards aren't even beating 590's by much...
i don't know what other things to try to adjust. I am not even worried about the efficiency right now. i have the voltages up so I could have high clocks and stable mining. Just now getting good hashrate.
The only thing i have not tried is installing newer drivers from AMD. Didn't want to abandon known-good drivers for other algos unless i had to.
guess I'll have to experiment with some different drivers.

thanks again Andrucrypt, you rock
🖖🏼
High voltage for Vega cards are bad idea, because they will drop clocks exceeding power limit. Just started to test my Vega64 on zergpool. With my settings(check them in OP) I'm getting 16-18MH/s per 250-260W(and again, not precise undervolting, just 1000mV for core).
ps: hmm, but looks less stable on poolside because of not optimal vardiff per one gpu.