4K isn’t all that different from 8K. Both are very difficult to run from a hardware perspective, and both have relatively little content designed specifically for those formats. 4K-displays that don’t cost thousands are going to have dismal specifications in almost every category besides resolution. It can also be difficult to cleanly utilize the screen real estate of a 4K display because of the ratio of resolution to display size.
Ultrawide resolutions are 2560×1080 or 3440×1440, which gives you lots of extra space to work in. 4k (“ultra HD”) resolution is 3840×2160. While that higher resolution gives you more space, unless you’re getting a 32-inch monster of a 4k monitor, you’ll have to scale the interface of your programs to display them properly. You’ll also have to be sitting at a very precise distance from your monitor in order to be able to appreciate a difference between 4k quality and something lower like 1080p.
A 4k resolution is equivalent to FOUR 1080p displays on one screen. Even as the cost of 4k monitors starts to come down, you’ll be sure to need one or two top-shelf graphics cards and a modern CPU to be able to just scarcely handle 4k. Ultrawide monitors tend to be about 40% more resource intensive than standard monitors, but unlike 4k, you probably won’t have to undergo major upgrades just to plug in an ultrawide.
Aspect Ratio Difference — 21:9 vs. 16:9 (4k)
21:9 aspect ratio is hit-and-miss for gaming. It’s being adopted more and more often by developers, but there are still plenty of games without support. That means sometimes you’ll end up with black letter-boxing on the side of your display to make things look correct. There’s a dedicated modding community to help improve this support. Some games will look great right out of the box, others might need slight fiddling to perfectly fill the screen. (Be sure to check if your favorite games support 21:9!) You’ll never run into a problem with a 16:9 aspect ratio, though you may run into issues finding 4K content to fill that space with.
Ultrawide Monitor vs. TV
There’s a world of difference in terms of input response lag when comparing monitors and televisions. Even so-called gaming televisions have considerable input lag, and usually unimpressive refresh rates. The few televisions that advertise themselves as having 120 Hz refresh rates are often unable to deliver on those figures, because a television needs a DisplayPort or HDMI 2.0 to deliver that kind of bandwidth, meaning your connection may be converted into a 60 Hz signal.
Even when you put aside the 22 ms of input lag that’s standard for most TVs, which is twice as slow as most gaming monitors, getting a TV means you’re going to end up with inferior image quality. Ghosting, blurring, screen tearing — these can all be eliminated with modern monitors. Televisions can, at best, put a band-aid on these types of issues.
So What Should I Get?
If you’re not concerned with image quality, refresh rates, and input lag, then by all means buy a large 4k television. But if you’re serious about image fidelity, especially when it pertains to gaming, then there’s no replacement for an ultrawide monitor.