Got bad news on RX Vega 56 - managed to do a test with the Beta Blockchain Drivers (solely released to fix the Dag file memory issue for the RX 580/480 and 570/470 GPUs).

RX Vega 56

-24% Powertune
HMB2 925mhz
Default Clock ranging between 1136mhz to 1260mhz.
PSU Efficiency is 90%
Power Draw 152watts

Miner produced a Claymore result of 35.4mhs for 153watts.

Pool shares 40 minutes never above the rate for 36mhs.
Pool shares next 40 minutes around the rate for 25.5mhs.

Average pool shares found averaged around 31mhs for Ethereum - the same as the main official drivers. The Beta Blockchain Drivers are for the RX 580s and RX 570s, when used on RX Vega GPUs they produce fake hashrate figures, which are incorrect by 4mhs.

Beta Blockchain drivers do reduce powerdraw by 13watts per GPU, compared to the official drivers for RX Vega 56. This is why people are using them!