Yeah multi screens are odd when it comes to games. For the most part it is almost like trying to play widescreen 10 years ago. Fortunately said people doing the widescreen stuff have since gone on to cover multiple monitors and crazy high resolutions (
http://www.wsgf.org/mgl being a good start there).
For day to day computing I can not do without multiple monitors, preferably three but two will do, especially if I can have a portrait one. If I am typing a document with references to another, editing graphics, editing video or doing CAD then I will first seek another monitor, and even go buy a cheapo graphics card if the machine I am using does not handle it. It is that much of a dealbreaker for a lot of what I do these days.
For games two monitors is not ideal as the middle of the screens would be where your crosshairs/the horizon is so you do want three, unless you have one monitor like a normal single screen game and another for inventory/map/radar/general data but there are not so many games that support such a setup, though nothing is stopping you from having extra info in a web browser/video player/chat window or something. These days most would probably look to something like the eyefinity from AMD for that sort of thing, back when the Matrox triple head to go (thtg) was the weapon of choice for those things that might not technically have supported it.
Also "4k at 60 fps" is easier said than done and not just because that is a lot of numbers to crunch. Many 4k screens (I will leave the discussion of the various types of 4k for later) will only do 4K at 30Hz, especially if they go out over HDMI (the newer revisions of HDMI will support it but they are not there in graphics cards or monitors, much less the ones mortals can afford). To that end you will probably then want a displayport setup or possibly certain types of DVI (most monitors will opt for displayport though). Though consumer 4k is quite literally 4 1080p monitors stapled together there are also things that are perhaps not as nice with them and dual monitors can still have some advantage.
The other side of that is 4K monitors if they are going cheap might not be as nice as what you can get for the same money in the 1080p or greater than 1080p but not 4k world. Most 4K monitors that go for sane prices will be TN type displays where you can get some nice IPS stuff for similar money back in 1080p land. TN does tend to come with lower latencies by default and modern ones do pretty well for colours and viewing angles compared to days of old but you might care about such things. Much like consumers subsidising 4K for me I would not mind them also doing it for colour calibrated monitors but it is a harder sell.
@
AncientBoi:
