I'm sort of just piling on at this point, but this Planar panel seems to have some image retention issues also.
I have an Asus 4k VG289Q right alongside and I'm doing direct comparisons with them both connected on macOS and Windows 10.
The 5k definitely has a bit more text clarity, particularly on macOS (Windows handles that better and it's a much closer situation on the Windows side - if not indistinguishable honestly). The one thing that is really obvious when running the Eizo monitor test on both, simultaneously, is that the consistency and evenness of the display and backlight is noticeably better on the Asus.
IPS glow is pretty well controlled on both.
The 5k panel has less off-axis color shift and loss, but both are fine for anything in the range of a person in normal usage positions.
I have the Catalina dynamic wallpaper running (of the island) and other than really really looking for it on very small rock details, it's a dead heat on the quality of the image. I honestly think most of the difference here is likely the glossy vs matte coatings - the latter of which does ever so slightly reduce clarity. Glossy is of course the winner on clarity and "pop". I still in my mind feel that I'm just having a very very slightly harder time with maybe some super light eye strain on the glossy though. It's hard to describe and probably pretty subjective.
I have to say - whatever Windows does with that ClearType setup they walk you through is really great. That process managed to get both monitors to basically look equally good on text clarity, which is a huge help to the 4k. It's sort of bummer macOS doesn't have more exposed controls around text rendering.