I picked up this Vizio 40" 4K UHD - http://www.rtings.com/tv/reviews/vizio/d-series-4k-2016
Looks great. Its does everything it's supposed to - 4:4:4, 60Hz at 4K (through one input only), low latency. However, there's no way it's going to be better for productivity than your two 27" monitors because you're going to have to put in a 150% zoom on the 4K, otherwise everything is going to be too small.
You're going to to have increase your mouse sensitivity because you have so much more real-estate to cover and it will take you days to get used to it.
The 150% zoom will screw with some games, and Windows often won't let you change it on the fly - it requires you to log out and back in.
Fullscreen games at 1080p look poor, not as good as a standard 1080p screen. However, setting Fullscreen Windowed mode, where the game is doing the scaling, looks as good as 1080p. I have not tested this extensively. The first thing I did after getting a 4K monitor was to purchase a GTX 1080 because I realized I never wanted to play at 1080p again. (Then I had to buy a new power supply, because my generic 750 watt couldn't handle it, then I had a slew of other issues unrelated to the monitor...)
I don't regret purchasing my 4K TV to use as a monitor, but I did end up spending a lot more money that I had originally planned (the GTX 1080, power supply) and also went through a lot more hassle than I planned (UI scaling, mousing, getting the colors to look right took days, "game mode" was causing me eye strain, blown power supplies, bad RAM, bad GTX 1080...).