[Tepix]

There are two generations of the Dell XPS 13, at first they had a 3200x1800 display, they switched to 3840x2160 last year.

In my opinion 3200x1800 at 13.3" is more than enough already (I own one) but I guess marketing wanted more.

[truncate]

Yes, I also have the old 2015 model (3200x1800). Definitely, good enough in my opinion too.

[Brakenshire]

Are they in the range where the UX size can be doubled without being too large?

[truncate]

Yes. 2x worked perfect for me at 4k, and its the default for hidpi settings I think. When I switched to 1080p I had to manually increase font sizes (not overall scaling) because the default size wasnt sharp/readable enough. Its pretty cool 4k now works so well out-of-box on Linux. It was nightmare in 2015.