This may be redundant, but a 27" 4k monitor with text scaling set to 150% (the Windows default for 4k) gives text that is quite readable to me, at my normal viewing distance (roughly 24"/60cm).
I admit that I'm currently using a 32" monitor, at the same scaling.
Older software (like Photoshop CS6) doesn't scale well for a 4k monitor. (There is supposed to be a work-around for that, but going to the CC subscription version eliminated the issue.)
One oddity: if you set the scaling to 150% with a 4k monitor, 4k YouTube videos will play in the browser at 2560X1440. You could set the scaling to 100%, and the videos will play at full resolution. The text will be too small, though.