I tried the RX 580 but had a few issues. First, it took a lot of trial and error to figure out my Lilu & whatevergreen kexts had to be in the /L/E/ folder to solve black screen issues (not just the EFI...KEXTS/OTHER folder). While the RX was easier to setup than my Nvidia card, it wasn't by much in my case.
I also couldn't get 60hz in 4K on a new Samsung TV. Unlike Windows, MacOS is fussy about 4K monitors and not all work well. I got 30hz no problem, but at that rate, fast moving video/screen objects looks choppy. Hacks exist for Nvidia but didn't see them for AMD.
I'm disappointed...I'd love to have the RX for Final Cut X. But I want the 1080Ti for Windows VR games. Right now, I can't get them to co-exist in the same machine so will likely return the RX.