Here's a setup we use for watching the two cameras using some old LCD's that we'd run out of room to store. This uses the remote X11 xvideo as I described above.
All 12 displays are run by one machine sitting behind the LCDs. It is a Dual P4 Xeon, 2.8GHz, w/ 1GB of RAM. It has an AGP GeForce 5200 and five PCI GeForce 5200s. It's an Xinerama desktop composed of six twinview'd screens. In this picture, both of the camera feed's being displayed are an mplayer process on another machine playing a v4l2 device and the video out is XVideo via remote X11 over gigabit ethernet. The left camera is running at 15fps (usb webcam limitation) and the right one is 30fps (real tv camera attached to video framegrabber.) Both streams are 640x480 scaled up (by the graphics cards) to 2048x1536. We don't have any perceptible frame drop. We did find that using Jumbo frames (9000 byte MTU) on the gigabit ethernet reduced the load considerably. We specify on the mplayer command line the geometry of the window it makes.
e.g, for the first camera:
mplayer -screenw 4096 -screenh 2304 -xy 2048 -geometry +0+0 <more mplayer stuff>
and for the second camera:
mplayer -screenw 4096 -screenh 2304 -xy 2048 -geometry +2048+0 <more mplayer stuff>
The -geometry and -xy lines, specifically, specify the size of the mplayer window and it's location on the screen.