Wouldn't that depend entirely on the resulting height of the monitor in portrait. A smaller monitor it wouldn't matter. The purpose of a curved monitor is to have the screen at or closer to square to your line of sight. If the monitor is large enough that you're having to look up at the top of it, then once that is above a certain height, a curved monitor will be easier. The optimum tilt of the monitor would depend on the height of your eyes are compared to the centre of the monitor. The 28" in portrait was rather nice. And 1920 pixels high. Three wide, or four wide...
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.
p.s. Coding. Going from a pair of 1080 28" to the 55" 4K, my coding output went up by a factor of three. Design nearly doubled. I could have more info displayed, so jumping around opening/colapsing from window to window for info was hugely reduced, and I had enough realestate to display all or nearly all of what I needed for what I was working on. Productivity was so hugely improved that I found something else to focus on when on the double monitor workstaion, saving core coding sessions and complex design for when I was on the 55" 4K workstation. The six-up was better than the double monitor, but for reasons I can't figure out, no where near as productive as when I was on the 55" 4K. When doing my own work on my personal 55" 4K plus 28", the core programming IDE goes on the 55" and email, manuals, browser and stack-overflow goes on the 28".