I'd say it depends on two things:
- how far you are from your screen and how good your eyesight is/how much attention you pay to details
- how your display handles scaling
I use a smaller (17.3") 4k display viewed from fairly up close and upsampling 1080p to 4k is very noticeable since the display defaults to bilinear interpolation and there is no way for me to change this. It doesn't look as horrible as the blurry upscaling of yore, but it is ugly enough to where I wrote myself a nearest neighbour (i.e. pixel doubling/tripling, etc.) upsampling tool for games/programs at <4k resolutions. As far as non-integer scaling is concerned, 1440p -> 4k looks alright, but the blur is definitely noticeable.
I've uploaded a small comparison of close up photos here (all images are in focus, sub-pixels are visible in the raw images):
https://imgur.com/a/GH1aNfp As you can see, the difference can be quite dramatic.
If you aren't after high refresh rates or ultrawide or anything of the sort, I'd suggest 4k over 1440p (if at all possible) even if you might not want to run games at 4k; it gives you more options when it comes to upscaling lower resolutions, and even if you stick with bad image scaling, the result should look better. For graphic design work, it's definitely a big step up.