I’m not quite ready to upgrade to a 4K (4096×2160 resolution) monitor yet, but if you are, Samsung’s 28″ 4K display is on sale for $400 (down from $700) for Cyber Monday.
At that size and resolution, it works out to 165 pixels per inch, which is very close to what we used to call “near letter quality” in the days of dot matrix printers. To me, this seems more practical than using a 42″ 4K television, and the refresh rate is much better.
Keep in mind you do need Displayport to drive a 4K display. Most video cards costing $100 and up have those these days, but even some Geforce 210 cards have them, like this Jaton.