No amount of googling reveals an MG279K to exist out there.
The PG278Q isn't under manufacturer any longer, as far as I know. There is a replacement PG278QR, but it is the lowest end QHD G-sync display from ASUS. Dell offers a better/cheaper option, and Acer still makes theirs as well. At that level I would look at the appearance.
PG279Q is more current, that is the AHVA 4ms panel with the G-sync 2.0 module. Again similar models from Acer in the XB271HU and the older XB270HU.
It really comes down to your GPU. If you have a high end Nvidia card, GTX1070 or up at least. Then 2560x1440 or 3440x1440 are within reach. Frame rates won't be amazing. Those panels really demand a GTX1080Ti at least. On the AMD side of the house, a Vega 56 is about as low as you can go. There are many more FreeSync offerings, but usually the same underlying panel as the G-Sync monitors, just a different scalar (which may not be as good for latency as Nvidia)
If you have anything less, you should be looking at 29" 2560x1080 or 24" 1080p panels with high refresh rates. 120. 144, 180, and now 240hz available. Though for 240hz you would be looking at GTX1070 and up again.
These products are expensive, so it is best to know what you are getting into.
There are arguments from hardcore gamers that the ultra wide screen is a two edged sword. On the one hand you can see more to the left and right. On the downside, you can look over to one side and not see something on the other side. It would also naturally lead to less scanning. Many games now offer adjustable HUDs for ultra wides, but not all, so some important information may require you to look quite far away from center as well.
I think 27" QHD is about right for the moment. And it didn't break the bank to get a GPU to handle it (I have a 1080 and a PG279Q). Now though, a very expensive proposition. Had 3440x1440 panels been available I might have considered it, but at release those were over $1,000, and I still paid $800 for the ASUS.
On the other hand. Nothing wrong with over-buying on a monitor. GPU prices will decrease, and people tend to keep monitors a lot longer than GPUs. I look forward to when I drop a new GPU into my system and get the absolute most out of my monitor, for now 90-100FPS isn't bad on max settings.
If you want a quick look at available monitors:
https://pcpartpicker.com/products/monitor/#H=85,240&A=1,2&W=2380,5500&r=344001440,256001440,192001080&sort=price&page=1
Standouts would be the Acer XG270HU, Dell S271DG, ASUS MG278Q. If you are sticking to the cheaper QHD panels.
Plenty of high refresh choices though. If you aren't seeking high refresh and just want UW, plenty of options out there as well.