[pheug]

Tried HP z27q for a month under Linux with Cinnamon, didn't like it. Being a DP 1.2 monitor, 5K resolution is implemented as an ugly hack using MST and two displayport connections. The system views it essentially as two independent monitors. Stuff like maximizing windows just plain doesn't work, you always work on half the screen, window panels are half sized, etc. Some work went into fixing user experience on GNOME, but for Cinnamon the maintainers are not interested in proper support for MST and I'm not interested in switching DEs. The situation is a better in newer monitors with DisplayPort 1.4 though, which gets rid of MST. But these are only Planar and Iiyama which you say you have problems sourcing. My monitor examplar also every so often would randomly flicker for a few minutes on a cold start, which also contributed to my decision to get rid of it.

My recommendation is to just get a 4K 27". Much more options and similar enough PPI, you would hardly tell the difference. Well, you won't have the perfect 2x scaling without stuff looking too big, but most desktop environments today support fractional scaling and/or you can play with your font sizes. I have 2x scaling now on 4K 27" with smaller font sizes, stuff looks about as good as what I had on 5K.