Who doesn't love more pixels? The more pixels on a screen, the more stuff you can see, right? Well, not quite. Not all 4K monitors are equal and depending on which one you buy, your experience will either be fantastic, or rather lacklustre.
The key concept to understand with a 4K monitor is a measurement called pixels per inch (PPI). Depending on what you plan to use the monitor for, the PPI of the panel can make a huge difference to quality. If you've ever used a smartphone and wondered why those little displays make text look so good, it's because they've got a high PPI. Take the Samsung Galaxy S7 for example - the 5.1in screen has a 2560 x 1440 resolution display. So does the Dell U2715H, which is 27in. Look at each of those monitors from the same distance and it's no doubt that the text and images on the S7 look much nicer, without any visible pixels. This is because there's 575 pixels per inch on the Samsung versus 108 on the Dell. There's so many pixels jammed into the one spot, the display looks sharper.
How does this relate to 4K displays? Well there are many 4K displays, all with 3840 x 2160 pixels (that's what makes it a 4K display), but in various sizes - 28in being a common size for the lower priced ones. A 28in 4K display has a PPI of 157 - keep that in mind compared to the 108 PPI of the 27in Dell. Such a high PPI, without image scaling, means very tiny text, almost illegible. So what's the problem: turn on image scaling and enjoy, right? Not so easy - when you scale the image up, you'll see a certain improvement in the quality of text, but you'll also reduce the amount of stuff you'll see on your screen. If say, you turn image scaling up to 200 per cent, that means what would normally take up one pixel on your display, now takes up two pixels, in effect turning your 3840 x 2160 monitor into a 1920 x 1080 monitor - but an amazing looking 1920x1080 monitor!
Simply put, if you want a 4K monitor for crisp text and don't mind sacrificing desktop real estate for it, get a 24-28in screen. The Acer XB281HK is a pick for the gamers, with G-SYNC support and a 1ms response time. For those after more colour accuracy for professional use, the BenQ BL2711U is a 27in 4K display with 100% sRGB and REC 709 color space coverage. For day-to-day use If you want a massive monitor for awesome screen real estate and the same PPI as a 27in WQHD display, go for something in the 38-42in range. The Philips BDM4065UC, BDM4350UC and Dell P4317Q are standouts.
Regardless of which 4K monitor you purchase, make sure your computer can actually handle all those pixels! At a bare minimum you need a DisplayPort 1.2 output - DVI and VGA just don't have the bandwidth required to pump all those pixels out. Your graphics card also needs to be able to handle the 3840 x 2160 resolution while maintaining a 60Hz refresh rate. Some graphics cards may only support 4K at sub-60Hz, which makes for a laggy experience and not worth the expense for anything other than TV or movies.
If you're a gamer and want to utilise your 4K monitor for some beautiful high-res gaming, make sure your GPU is up to scratch. For example, the popular Grand Theft Auto 5 requires at least a GTX980 to work at 4K with a reasonable framerate (i.e: 60fps) - and that's with the quality turned down to medium/high.
Godspeed if you plan to game at 'ultra' quality at 4K. It's certainly worth searching for benchmarks of your favourite game running at 4K, to make sure you've got the right graphics card setup to ensure you're not hit with a slideshow when playing it at 4K.
Nvidia's new GTX1080 will help immensely for those wanting to game in 4K.