Got my Vega 56 in today (Sapphire reference model).

It's WIERD - to get it to get anywhere near the officially specified "1590" core clock, you have to kick the power limit WAY up (+30% at least in Afterburner) AND you have to UNDERVOLT it quite a bit (-100mv ballpark) - and even THEN it won't get to 1590, though I did see mid-1500s after a bunch of settings work.

In stock form, it's not quite a 8 Gigakey/sec card (for perspective, the GTX 1080 ti can hit a little over 10 GKeys/sec with some overclocking).
Maxed out, I saw about 9.5 GKeys/sec though - which is not bad at all for a $460 card compared to the 1080 ti at $700+, and quite a bit more than the GTX 1080 manages in the same price ballpark.

Card also runs AMAZINGLY cool unless you push it very hard - never much past 55C at stock settings with less than 55% fan, and the settings I found to make it a 9GKey/s card was only pushing it to about 62-63C at under 68% fan (I run a straight-line "fan curve" in Afterburner by default that is "all in" at 80C and drops 20% every 10C below that).

I estimate that a stock 56 will exceed 1 million RAC by a bit, a pushed one should get into the 1.3-1.4 million RAC ballpark - in other words, a SINGLE CARD can exceed all but about the top 3 or 4 machines currently working Moo Wrapper.

Given wide reports that the air-cooled Vega 64 clocks higher reliably than the 56, and that it has 64 CU instead of 56 (1/7'th more cores), I am ready to state that the Vea 64 SHOULD be the current Dnet/Moo Wrapper single card performance king - especially if someone wanted to put out the kind of money to get the WATER COOLED version, which supposedly clocks a LOT higher than the air-cooled version.

Looks to be ~10Gkeys/s for Vega64

I've just attached it to Moo! :)

Have you optimised it for Dnet/Moo?

What I found on my 56 was that it wanted quite a bit of undervolt, along with the usual "drop the ram speed to the minimum" and a bit of set power limit up, to get optimal keyrate while keeping temps fairly low.

I'm running mine as follows:

Core no OC
Memory P3 @1100Mhz
Core P6 @950mv P7@1000mv
Memory P2 @950mv P3@1000mv
Target temp @65C
Max temp @75c
Fan @10-4900rpm (full range available)
Power target @50%

With all this it's currently 100% stable, computer running 100% LHC@home on CPU and 100% Moo! on GPU, power consumption from the wall hovers around 330-360W (Seasonic SS660XP2 PSU).

I got mine at MSRP so not complaining :)

Bumping memory up for Moo Wrapper work is a waste - the entire Dnet client AND data fit into cache memory on anything remotely recent in a GPU.