I'm on:
AMD Ryzen 3900X
AMD Radeon 6950XT
64 GiB RAM
Arch Linux
Proton Experimental
The VAB can get up to like ~80fps. I managed 10 or so at launch, up to 40 in the air and sub-10 on the way down.
The UI looks like it's supposed to be pixel-perfect but it's misaligned (apparently this is just a 1440p issue as my Windows-y friend has it too).
I tried to force Vulkan with the command line options but that just gave initialisation errors.
All in all, I'm just happy it booted on day 1. It would be great to get a native build, or at least one with Vulkan enabled so I can try that.