I'm using a single 44" Vizio 4K TV for my main monitor attached to a Dell XP 15 laptop which acts as a second monitor (it also has a 4K screen).

I picked 44" as the optimal size for me by standing 3 feet in front of all the 4K TVs at my local warehouse store and seeing what sized TV let me see the entire screen without swiveling my head - 48" was just a little too big.

My 4K screen works really well in Windows 10 other than a couple of old apps that don't to font scaling for their title bar correctly. I have the TV scaling at 125% and the laptop scaling at 250%. I'm not sure what an 8K screen would do for me as a programmer.