I just upgraded from an AMD 570 to an AMD 5700 in the Clover/Asus Z370-G/i7-8700k setup. With 2 2560x1440 monitors attached, in Starcraft II (2560x1440, ultimate/extreme everything, Metal), I notice a small performance uptick, but not quite the night-and-day difference I was hoping for. This is a good choice if you do a lot of Windows gaming; for MacOS I don't see a huge benefit.
For Windows I see 100-140 fps (on a 144hz monitor) and for MacOS, I see 60-80 fps, both in SC2, in a very quick check/test; I'll evaluate more as time goes by. Superposition will be the next benchmark; I expect it to be similar in performance to a standard 1080; maybe a touch less. At a higher price compared to the 1080, two years later, I admit this is a difficult pill to swallow.
I've done no BIOS flashing or made any other changes, instead testing for stability first.
I've had no driver issues, crash issues, blue/black screens, etc., as some have noted / complained of in Windows (Or MacOS for that matter).
As I have the iMac Pro "setup", I did need to change Clover bootargs to add the pikera bits. No other changes were required.