It's my first post on this form and I take the opportunity to thank you all (Mythic in special) for you knowledge sharing.
Below you can find my experience with both RX Vega 56 and 64 version mining Monero @ 1800-2000 h/s:

Both my rigs have the same configuration except GPU type:
-  8 x GPU (8 x RX Vega 56 on first rig and another 8x RX Vega 64 on 2'nd) , Biostar B250 BTC-PRO, 8GB-RAM DDR4, SSD 120GB (65GB Virtual memory in Win10).
-  Software config: Blockchain driver, Soft PPT in registry, disable-enable display adapter after restart,  cast miner 6.0
-  Result:~1800 H/s on all 8 pcs Vega56 and ~2000 H/s on all 8 pcs Vega64
-  Print screen with the results:
https://drive.google.com/file/d/1b8Y2QJZDgDmOyhgedVEKHJaa3GGPeaPtBQ/view?usp=sharing
https://drive.google.com/file/d/1LlhIxuc4MFVbUog50BKigv-aqV-RXuCp6g/view?usp=sharing

Coming soon: please be prepared for one of the most interesting rig (8 GPU in a semi open case with  a horn on top for hot air exhaust)