A few things to consider
Chroma subsampling 4:4:4 (for clearer text)
Response time (for faster moving images / gaming etc)
Bezel size (for aesthetics)
Brightness/Contrast Ratio (Will you be in a bright or dim room? If its a dark room then get one that produces better blacks for when watching movies or dark charts. If its a bright room then a bright TV that handles reflections is important. Viewing angles not that important for 4K TVs as monitors).
Be careful of size also, 55" would be too big for most desks and sitting distances. I have 43" and I sit more than a metre away. Any bigger would be uncomfortable.
To reduce eyestrain turn down the brightness and backlight to 0.
Most 4K TVs will display in 1080p 60Hz but to take full advantage of the screen real estate you obviously want a video card that supports 4K resolution.
The TVs software is important also but wasn't a deal breaker for me. LG has better software and remote than Samsung.
Is your 43" a LG Smart TV and what graphics card are you using.