Hey guys, I'm currently looking at buying a cheap 40 inch Korean 4k monitor to add to my triple 1080p setup, partially to have a nice luxury, but more so to expand video making options, allow for 4k optimizations in game design, and use the large size to increase productivity.
So lets go to where my questions are. Would this be a worthwhile investment? I'm not professional enough in game design for game design to sell me, and I'm not sure if the 4k video options are worth it, as I don't know how popular 4k YouTube is, or if the productivity gains over 1080p are that great.
That leads to the next question, would a high quality 1440p monitor at say, 32 inches be a better option? Or should I stick with my three monitors I'm using now?
The left and right screens are two IPS 1080p ASUS VS239H-P monitors, and the center is a TN, 144hz 1080p ASUS VG248QE. Any help would be appreciated.
Well...
I'm a bit in the right hand tail on this subject (see my rig), but for me the 43" 4K monitor I added to my battle-station was worth it. Beyond game design and 4k video, what are your use cases?
I'm a VERY visual person. I like to have all my research (including multiple instances of my course text open to different sections) all over my screen. For this, the big center monitor is invaluable.
Again, more use cases would help. Also, 1 4K could replace x3 1080's in productivity. I've been busy with work and school, so I haven't had much opportunity to game on my 43" 4K. I suspect it will be fine. I play Blizzard games. I also purchased Stellaris - that might be wild on a big monitor. One use case that I am looking forward to is multi-boxing. 
Is it worth - only you can answer that.
Currently I have a 40" 4K display in the middle, a 27" 1440p on the left and another on the right in portrait mode. I quite like this set up.
IMO 40" 4K is really glorious. Content consumption, gaming and productivity is great and you don't need any scaling meaning you get plenty of space. I would recommend it highly as I'm sure would @Skelterz but only you can make the decision if it is "worth it."
When I got my 40” 4k I just stopped using my 24" 1080p, whenever I needed to I would just put windows side by side or however.