Maybe it was just coincidence, but I had a 1300 hash rate at one point until I upped virtual memory to 32GB.
This is possible. Current community understanding is that you should have 16GB Virtual Memory for each Vega. I made the mistake of getting 32GB of physical RAM, and I'm only using 10% (more if I have other programs running like HWinfo64) - never more than 8GB so far.