I confused this thread with another one and posted some related comments on that other thread...but let me try to respond more directly.
First... Regarding the "gaming" monitor. One thing to keep in mind is that gaming monitors are heavily designed for very fast refresh rates rather then actual sharpness and colors. that isn't to say necessarily that they don't have superb colors and sharpness, you have to read the reviews to find out, but generally, their emphasis will be on fast refresh rates. And you'll likely be paying a premium for that as well.
Business class monitors are really the ideal for us. I would say that perhaps even monitors designed primarily for photography or video work could be good also, but anyway you basically have to read the reviews of every single monitor to find out about all that, but I personally like business class displays myself..and the higher end of the range where they could be pretty good for photography work or video work, but a truly discerning photographer might hymn and haw and say there are better displays with truer colors, etc.. ok fine...but we really don't need that either. For what we do, what we want more than anything are very crisp and clear lines and fonts. And I personally like excellent colors and excellent black levels and contrast, because that ends up easier on the eyes when properly setup. That's just me.
A gaming display may or may not have the absolute crisp lines and fonts (read the reviews), but generally their emphasis will be on frame rate, which is not an issue for us in DAW work, and not even for watching videos at 30fps.
HiDPI is hard to explain, I would have to write a long post to explain it. Google for more info about that. its built into both Windows and MacOS. Apple made use of this tech ever since it started coming out with its Retina displays. suffice it to say that it makes everything smoother and nicer. It provides a lot of options to use different scaled resolutions with much less jaggies then if you were just simply scaling the resolution without HiDPI. With a 32" 4k monitor (or 5k or whatever) you definitely want to find out how to use HiDPI..trust me you will love it.
I highly recommend a software product called SwitchResX for setting up multiple HiDPI resolutions that you can easily switch between on the fly depending on your task.
Note however that the Ultra-wide screens, which are often labeled as 4k or 5k, they do not have enough pixel density to use HiDPI. So if you get an ultra wide like the 49" you are considering, then you will not be using HiDPI. The key to using HiDPI is when you get a monitor that has a PPI spec higher than about 120 ppi, then its a candidate for using HiDPI and without HiDPI, that monitor's fonts would also simply look too small.
This calculator may be helpful: https://www.calculatorsoup.com/calculators/technology/ppi-calculator.php
The 32" 4k monitors at 3480x2160 have a PPI roughly around 130 ppi, which generally if you run it at its native unscaled resolution, the fonts will all be just too darn small. You can scale it without HiDPI, but there will be unsatisfactory jaggies. if you use HiDPI to scale it to a lower display resolultion, then all the lines, fonts and curves will be intelligently filled in so that you won't see jaggies. that's mainly why Retina displays look so darn good. They have a very high hardware PPI, even higher then 130 ppi actually. But the HiDPI tech basically scales things to a high density monitor much better...so you can scale that monitor down to something like 3008x1692 and it will have fonts that are big enough to read quite well without nearly as much jaggies as you'd get by scaling it down without HiDPI.
The old Apple 30" Cinema Display had a PPI density of around 100 ppi. if you generally liked the size of fonts on that monitor, then that would be the native hardware pixel density that would get it. Most likely the 49" ultra wide you are talking about has a pixel density close to that... The Dell you mentioned, which is a very good one by the way, has a 5120x1440 with ppi = 108. I personally feel that is still in the range of decent sized fonts. 110 ppi is about as high as I can go before starting to squint too much. But anyway, the point is, that monitor does not have a dense enough pixel density to even use HiDPI at all. You would need something more like 120 or 130+ of pixel density before you can realistically use HiDPI tech to scale things down in a nice way. But...there is not going to be any need to scale down the Dell 49, it already has a good font size in general.
The downside of that, is that you won't really have the option of scaling it up or down on the fly using HiDPI, like you would be able to do with a 32" 4k or 5k display. with those, you can use HiDPI and choose form a dozen different resolutions depending on your task at the moment.
I personally will probably have an ultra-wide eventually..I like the concept, but I would mount it lower and angled back so that I almost look down on it..and can look over the top of it at a bigger monitor on the back well. Don't forget audio monitor placement also where will they go with an ultra wide?
But we will not have those big ultra-wides with HiDPI capabilities really until some more years go by, current hardware is just not really there yet. We will need 6k or even 8k monitors with appropriate GPU's, etc.. and that is somewhat possible for big bucks, now, but hardly worth it for what we do right now. All that would require more CPU use too, so its a diminishing return after a point; It may be a while before its common place to have that much graphics power in a desktop..I personally think 5k will be it for a while... which means...large ultra wides will simply not be able to use HiDPI anytime soon.
When I was looking into this a year ago, I liked the Dell a lot. There is another 49" ultra wide I seem to recall which also had high reviews, but I don't remember the details now. each year there is new stuff, so you will have to let us know what you end up with.
I think its a highly personal decision about whether to use a single monitor or dual main monitors or an ultra-wide, etc. I personally don't like looking at a screen off center. I want my primary monitor directly in front of me so my neck is neutral and not turned to the side most of the time. That's my personal choice. When you go to bigger dual monitors, you'll have to worry about your audio monitor placement and more side to side turning...and maybe that is the case with ultra-wide too. I tend to think 1440 is also not quite enough vertical space, as someone else already said. I personally am using 32" 4k with HiDPI scaling options...and most of the time its running at 3008x1692 HiDPI mode...which has an effect ppi of 108 ppi (exactly same font size as the 49" ultra wide), but note that it has more vertical space...and I still have the option to rescale the display to various different HiDPI resolutions. I think I probably still prefer this...
The only thing is that if I had an ultra wide, I feel like I could mount it lower and angled back and look over the top of it at a monitor on the back wall easier...so I am thinking about that setup in the future maybe. But I also really like the HiDPI options of having a dozen different nice looking resolutions to choose on the fly.