I don't know of many games that can support 2 monitors. If you are planning on playing 1st person shooters or 3rd person shooters, then you really want 3 monitors and a very powerful graphics card.
Playing with just two monitors means the targeting reticle / player character will be divided onto both screens separated by the bezels. So it's either 1 monitor or 3 monitors. I prefer playing on a single monitor.
Playing at 5760x1080 resolution requires some serious GPU power. A single GTX 680 would give you pretty good performance with medium quality graphic, but if you wanna max out your graphics with that resolution, then you need to look at something equivalent to a GTX 690 for decent performance.