Even 4k turns out to be overkill if you're looking at the whole screen and a pixel-perfect display. By human visual acuity, 1440p ought to be enough, and even that's taking a safety margin over 1080p to account for the crispness of typical text.

1440p is enough if you haven't experienced anything else. Even the jump from 4k to 5-6k is quite noticeable on a 27" monitor.

I switched to the Studio Display XDR and it is noticeably better than my 4k displays and my 1440p displays feel positively ancient and near unusable for text.