I get 519h/s with single watercooled RX Vega 64 8GB on stock. Driver 17.9.1 CM 12.6
That is quite good. But it is still worse than the nVidia 1080Ti.
For the power usage it's pretty BAD - and slower than many GTX 1080 much less getting completely blown out of the water by any 1080ti.
On the other hand, there are reports that Vega does well on Monero (XMR) mining.
Is that very efficient on XMR?
I remember seeing someone claim 1800 hash/sec for a Vega 64 on Monero, and they didn't have the thing optimised yet.
That's THE highest performance out of any single card period, though there are a very few high-core-count CPUs that can match or beat it (Top-end Threadripper can match it pretty close, ANY Epyc can beat it, and I think a few of the top-end Intel Xeon server CPUs can also top it).