The vega 56 is a card deliberately limited to stop it being near the vega 64 . The memory cant go past 1000 mhz and that means the performance is throttled, apparently mining relys on memory bandwidth even more so I would guess it'll show in results.
Rx580 is still the best for power use. People saying Volta might be good at mining, that is next year
you mean core? memory could go to 1900, apparently, but then power goes to 290w, hashing at 34-36 Mh/s, which is bothersome for $750.
https://hothardware.com/news/amd-radeon-rx-vega-mining-block-chain-ethereumI say, f-k Volta. They already "screwed" up once, will not wait again.
Nvidia is so much better, low power, mining soft is super stable.