The highest rez I have ever heard of on a commercially available monitor is 3840x2400 (QUXGA-W mode).

Check out a monitor that does this: http://www.iiyama.com/product2/AQU5631DTBK.htm

At 22.2 inches, that ain't a particularly big area to spread nine million pixels over. Imagine the image quality. Also, imagine the sort of silicon it would take to push around Quake in that resolution...