Note that if you Alt+click the "Scaled" resolution radio in the display preferences you will see many more resolution options than the default 5 (source: Apple support article "Using 4K displays, 5K displays, and Ultra HD TVs with your Mac").
The options depend on the maximum resolution of your monitor and possibly your Mac graphic card/Mac generation etc.
MacBook Pro (Retina, 15-inch, Mid 2015) + LG 27 inch 4K monitor
Full list:
- 3840 x 2160 (4K)
- 3360 x 1890
- 3200 x 1800
- 3008 x 1692
- 2560 x 1440
- 2304 x 1296
- 2048 x 1152
- 1920 x 1080 (Full HD)
- 1680 x 945
- 1600 x 900
- 1503 x 846
- 1280 x 720
- 1152 x 648
Macbook Air (M1, 2020) + SAMSUNG 28 inch 4K monitor
(Full monitor model: U28R550UQRXEN)
Full list, including "low resolution" modes:
- 3840 x 2160 (4K)
- 3008 x 1692
- 3008 x 1692 (low resolution)
- 2560 x 1440
- 2560 x 1440 (low resolution)
- 2304 x 1296
- 2304 x 1296 (low resolution)
- 2048 x 1152
- 2048 x 1152 (low resolution)
- 1920 x 1080 (Full HD)
- 1920 x 1080 (Full HD) (low resolution)
- 1680 x 945
- 1600 x 900
- 1600 x 900 (low resolution)
- 1504 x 846*
- 1280 x 720
- 1280 x 720 (low resolution)
- 1152 x 648
* - yes, it is 1504 vertical while above this resolution had 1503 vertical 🤷♂️
And to answer your bonus question:
I am guessing that you use 2560x1440 on a 27-inch display now.
If so then to be comfortable you should get also 27-inch 4K monitor and use scaled resolution from the list above that will "look like" 2560x1440.
You will get the same screen real estate and the same size of everything, just sharper.
However, performance will be noticeably worse, in form of a delay after you type something and before it appears on the screen. Of course it will be in the range of milliseconds, but you will notice it.
Update: The delay I wrote about above was noticeable on the MacBook I had then (2015 Pro 15 inch without a dedicated GPU). With my current one, a 2018 Pro 15 inch with a dedicated GPU, the delay is not noticeable to me (but of course it's a subjective thing, you may notice it).