I interconnected 16 2560x1600 monitors and 4 AMD Radeon HD 7970 video cards, and I use full-screen mode at 10240x6400.
This has a total of 65,536,000 pixels.
I think it's possible to make a display configuration like this, since each video card supports 4 monitors, but it'll probably require custom software to divide up 25% of the screen to each card.