Well maybe I'll sell my damn GTX 1060
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.
Probably the 4K 60hz on the TV depends on the HDMI, and macOS doesn't work well with HDMI2.0, so you have to use DP to HDMI adapter.
I have the 5K monitor that's why I am planning to switch from the 1060.