I have the 43" Sony X8000D 4K TV and I've used monitors before, but ever since I have switched to TV's it has been a much better experience.
If priority of the PC is competitive multiplayer gaming, go with a 144Hz Monitor.
If the priority is entertainment (watching movies and series) + casual multiplayer gaming + single player campaign mode gaming, then definitely go for a TV.
Keep the size around 43" as larger than that, sitting on a PC table and a chair that's 1.5 meters away you don't want something bigger.
You want a 4K TV, that can do 4:4:4 Chroma Subsampling, with 10Bit HDR. Both of the TV's you suggested above have all those features. And the X85D is definitely the better TV, however the smallest size it comes in is 55".
The X80E is the new version of the X800D (also known as X8000D in the Asia Pacific region).
If you're sitting more than 3 meters away from the TV, I'd say go with the 55" X85D.
If you're sitting 1 to 2 meters away from the TV, get the 43" X80E
One final thing, the best thing about the X800D (the older model which I have) is that it came with a VA Panel, while the larger versions of the screen (the 49" and 55") both came with IPS Panels.
The VA Panel has deeper blacks, which is a big advantage. However, the colours get slightly washed out as you look at it from different viewing angles (so if you're not sitting directly in front of it, the colours get a bit washed out), for me that didn't matter at all because I am using it as a monitor, so it's directly in front of me. The IPS Panels don't have deep blacks, but their viewing angles are great.
I am not sure if the 43" X80E is still using the same VA Panels as the X800D or they switched to an IPS Panel.
So slightly above this range, you have the Samsung KS8000 55" and the newer KS8500 (which use quantum dot technology) they're better than the Sony TV's above. And if you want true deep blacks, you have to go with an LG OLED TV, but they're very expensive usually (however, they are by far the best, and jaw dropping in their quality). Every time I go to a friend of mine and watch a movie on their OLED TV, I feel like throwing my TV in the bin (even though I really like it). It takes me a day or two to readjust to using my TV again.
Stick to your price range, and in your price range I just gave you the pros and cons.