4k at 1x produces UI that's too small, 2x scaling is too large for a 27 inch monitor. 1.5x sizes everything like a 1440p display but you still get the higher resolution rendering at 4k.
Fractional scaling _is_ rendering at the 'proper' resolution of the display. It can be challenging to workaround some issues like how to deal with window sizes that scale to a fractional native buffer (i.e. a 501 logical pixel wide image becomes 751.5 physical pixels?). Apple decides 'no' to native fractional scaling, so does GNOME unless that's changed recently.
