I would personaly go for 1440x1080 on the main, and 3 windows of 480x360 on the right.
This preserves a good aspect ratio ( 4/3, like a TV i believe) and allows you to have the same ratio on all wows making mouse replication perfect.
if you can, still keep the resolution the same on all windows (1440x1080), just reduce the screen size of those one the right.