I see Vega 64 benchmarks 34.4 mh/s for eth.
I would think the cards can do 43-46 mh/s if a good bios with memory timings is applied.
One would be better off buying 2 x 470 or 2x 480 or 2x 580 or 2 x 570 or 2 x 1060 3gb samsung memory cards.
The performance per cost would be cheaper if going this route.
Currently I see new 1060 and 470 cards under $240. At 22-28 mh/s per card, this is the best "new" card deal out there.
Where do you live?
In US, I only see those for $270-400, maybe you can find cheaper on ebay, but not easily.
I'm in Silicon Valley.
The nvidia gtx 1060 3gb I've seen sell for $215 to $230 on amazon (wanna get the Samsung memory ones).