It's complicated. For me it's about how smooth the text is and how consistent the experience is. 4k with 2x (integer scaling) is a pleasant balance of crisp rendering and appropriate text size.

The lower resolutions would require non-integer scaling and so far my experience doing that in Linux environments has been very poor. I don't expect this to be a smooth experience any time in the near future. I'd love to be proven wrong though.

The difference is huge for me, especially for reading texts. The rending quality is night and day.

Between 1080 and WQHD, sure. But between WQHD and 4k?

Yes, I can definitely tell. I have owned both WQHD and 4K laptops. At least for text, I can tell the difference at first sight, and I’m more comfortable with 4K.

Both are fine from a DPI standpoint, but some people prefer the size of 4k@2x to WQHD at 1x or 2x.