IF you want to go for Cryptonight, stick with Vega56. and BC Driver
Max. 4 cards/Rig. More makes problems. Use the registry patch for voltages. Runs best at 1202 mhz GPU / 900-940 MEM @850mv.
My Vega56 run at 140 Watt each, doing 1650 h/s each with AMD-STAK-XMR,
or 1950 h/s at 275 watt each 1630 GPU / 1100 MEM with Vega64 Bios.
Check out the "monero and vega ultimate guide" post on reddit, I have 3 vega 64's and 1 vega 56 running generating 7700h/s on cryptopnight pulling 670 watts at the wall that includes the motherboard, harddrive and 2 addon fans.
you can seriously undervolt these cards man, theyre giving me great returns.