I picked up a Vega 64 and installed successfully. A few notes:
* It's a much bigger card than the 1080, and only just fits in my MicroATX case length-wise (
https://www.amazon.com/gp/product/B01N05CPU8/?tag=tonymacx86com-20) with the current positioning of my fan. Photos attached. Hoping this does not result in temperature issues. Might actually be able to solve easily by moving the fan up.
* I installed Lilu and Whatevergreen as recommended for this card. However, I had 3 kexts installed that conflicted with the latest versions of Lilu and Whatevergreen: IntelGraphicsFixup, NvidiaGraphicsFixup, and Shiki. This resulted in a bootloop. Removing the 3 deprecated kexts resolved the issue. See
https://www.tonymacx86.com/threads/new-lilu-and-whatevergreen.256602/#post-1782037