There is a correlation with monitor sizes and resolutions;
1080p - up to 27",
1440p (2K) - min 27",
2160p (4K) - min 32".
Meaning that e.g 27" 1080p would look quite bad, since pixels would be drawn out and you could even see individual pixels (depending on sitting distance). Hence why 27" monitor is better off with 2K reso. And with 4K reso, anything below 32" would be too small, to actually benefit from 4K. Might as well pay less and get 2K resolution monitor instead.
Any recommendations if I decide to step up to 4K... in the 27"- 30 "something" range?
Sure, but options aren't that "pretty", e.g
27", 4K, flat, 60Hz, 5ms, IPS - Samsung S80A LS27A800UNNXZA,
amazon:
https://www.amazon.com/dp/B09FRCXSJK
32", 4K, flat, 60Hz, 4ms, VA - BenQ EW3270U,
amazon:
https://www.amazon.com/dp/B078HWBGH5?th=1
32", 4K, flat, 60Hz, 5ms, VA - LG 32UN880-B, (good business/work monitor with it's arm and rotation feature, pricey too)
amazon:
https://www.amazon.com/dp/B08BCR862L
To put it short, under 500 bucks, there are no 4K monitors that have higher refresh rate than 60 Hz and lower response time than 4ms. While decent for business/work use, those aren't good for gaming use.
Almost proper 4K gaming monitor costs easy 650+. E.g:
27", 4K, flat, 144Hz, 1ms, IPS - LG 27GN950-B,
amazon:
https://www.amazon.com/dp/B08BCRYS6B