I use a corner desk and its amazing. I have always felt way more comfortable with enough room to fully rest my arms on the desk while typing. I can't STAND small desks where my arms are in the air or on my lap when using the keyboard. Way too uncomfortable for long work sessions and especially long gaming sessions.
I am 42 and I have had this desk since I was 21 lol. I can't get rid of it even though its gotten slightly beat up. It simply too comfortable. It doesn't even work in my home office all that well because I have it facing OUT of the corner so I can watch my TV while I work, which is across the room.
Here are a few pics for reference. Highly recommended configuration! (Note: I could move the monitor back at least another foot to 1.5 feet on this desk from the position shown in the pics below.)
In college, I used this desk to game with a 55" tv where the monitor is now and it never felt too close. Considering a new Nvidia BFG 144Hz HDR 4k TV as a replacement when the next round of GPUs come out that can (hopefully) push 4k at 120+ fps like the 1080ti does with 1440p currently. Until then I'll stick with my Asus ROG 27" 1440p 144hz.
If you are looking for a 4K monitor for gaming NOW - id suggest at least 32" or bigger. You won't feel like you are turning your head IMHO - I didnt notice that problem on my 55", but for some games, I would change INI settings to move things like minimaps and health icons closer to the center of the screen. Monitors that are smaller than 32" at 4k look too small (on screen) IMHO.
I tried a 42" TV at one point too (back when 1080p was the thing) and it felt just right for an oversized monitor. I am guessing that would be an amazing size with a high refresh rate 4k monitor. For competitive gaming, my 27" at 1440p is perfect though. For comp gaming on 4k, id probably go no bigger than 32".
These days though, id consider going ~50" with one of Nvidia's new BFG 4k HDR 120 - 144 Hz monitors, assuming the HDR at that size is still not causing lighting issues.
I tried to find and link the Linus video of him playing on a new BFG and showing how the lighting on HDR finally worked properly. It included clips of him playing on other 4k HDR monitors where the lighting looked all goofy with HDR enabled - i.e. it would create a "box" of brighter light around the mouse area where it was brighter there and darker everywhere else. Especially jarring in darker areas in game. He was happy to report the Nvidia BFGs did not have that problem.
I should also state I own stock in Nvidia and so far it's more than paid for my PC building obsession - and I have always been a huge fan of their GPUs - so I am quite partial to them. (But I do own stock in AMD as well lol.)