It is safe to say that most cryptocurrency miners have been relatively unimpressed with AMD's newest lineup of Vega GPUs. While the Vega Frontier Edition scores a decent 34 MH/s on ETH mining, it consumes around 300 watts of power which makes it extremely inefficient for mining compared to the older RX 400 and 500 series GPUs. This inefficiency coupled with a higher MSRP makes the Vega series of GPUs a rather unattractive option for cryptominers.

It is possible, however, that the new RX Vega GPUs will be a very different story. According to an unofficial rumor from an employee at Overclockers UK, RX Vega GPUs will be able to mine Ethereum at anywhere from 70-100 MH/s per GPU! This would be a massive step forward from previous GPU generations, and would mean that RX Vega chips would be extremely lucrative for cryptominers. Personally, I find such a large increase in performance rather unlikely, especially considering the rather lackluster performance reviews Vega has gotten up to this point. At the same time, this is definitely a story that I will be following very closely, as will any other cryptominer. If it turns out to be true, it could turn the whole mining world on its head in just a couple of weeks.

Source: https://forums.overclockers.co.uk/threads/gibbo-vega-preorders.18788127/page-6#post-31026435