Vega is ... hot. In stock it takes about 400-450W in dual, 300-350W in ETH-only mode at about 33MH/s. And it's throttling like hell. It's very good in dual mining mode, but it's too hot.
Undervolt it - DUH. I forced mine to never go above 1.025V, and she mined Sia under Linux at 1600Mhz stable! :3
I'm noticing that the core clock is less important than the memory clock.
I'm a little nervous about how much voltage I can give the HMB2 though... These Vega FE's are the first GPU's I've every messed with voltage and clock settings. I rarely overclock anything, but since I bought these cards to mine with and they represent 2/3 of my mining GPUs I want to get as much out of them as I can. They're also all of my disposable income for the next year so I don't want to ruin them and risk getting turned down on a RMA.
Currently at
852MHz GPU Core clock (My profile is setup for 1347MHz as the high end, but the GPU won't go past 852)
Memory is 1125MHz @ 1125Mv
GPU temp is 68C, fan is at 2779 RPM (~>50%)
Genoil is reporting 25.95 - 31.15 MH/s, but not enough run time to cite ethermine.org values.