If you calculate the pixel per inch, the 55" monitor has slightly worse resolution.
I like the new Samsung U32H850, 32" monitor.
it has excellent 4K resolution, and cheaper then its older model S32D850T (2K resolution only).
Careful with calculating DPI ratings using nominal sizes like 28" and 55", and in using published specs.
With my monitor, when you size something to be 100 mm high on the 55", and it spans across both monitors, its height on the 28" looks the same, but measures 97.8 mm. And I can't see the difference at my viewing distance; but then I notice that the 28" is an inch or so closer to me, which would account for their appearing to be the same size.
A friend had a 4K in something around 32". Amazing for photos. Graphs scaled up to width looked great. Standard sized items were too small to see; he had to scale them up or lean way forward and squint a lot. If you treated it as four monitors (four 16" monitors anybody?), the displayed info was simply too small. He moved to a 50" 4K.
With 4K, we're way beyond "better" or "worse", as there's so much info available. Are you looking to see what you're currently seeing, but with finer detail? Or are you looking for more realestate to have more info displayed? So more importantly, is how it will look displaying what you'll be looking at (reading) with that DPI and
at your final viewing distance.
Like when I go for 65" 4K on a bracket on the wall, I'll be getting near the same pixels per angle of view as the 55" 4K sitting out near the front of my desk. My perceived size of displayed objects will be near identical. (and I won't have to rethink and modify my platform's GUI)
You want to see something you'd be looking at on that DPI, preferably that exact monitor, and
at your final viewing distance. It would be a huge pain to calculate and for people to work with, but think DPI per MOA. Which is what viewing your type of info at your final viewing distance allows you to see what you'd get.