I've been using a 55 inch 4k TV [1] for the past year.
Its a matter of preference, but I prefer more usable space over DPI. I have found at this resolution pixels are small enough that they do not bother me. It takes some tweaking, but if setup right, text quality is indistinguishable from a "real" monitor. Its the rough equivalent of 4 27-inch 1080p monitors arranged in a square.
To get an idea of the size, here is a picture of me sitting next to it. [2]