A single 30" monitor has a resolution of 2560x1600. If you split it up into 1/2 of the monitor being your main, they get 1280x1600, then the other 1/2 can be further split 4 ways - so each alt gets 640x800.

Hmm. If you switched the monitor to portrait mode, that might actually be pretty playable (1600x1280, and 4x800x640).