I've got a 3 monitor setup going on with an HP s52031(via VGA), an AOC TFT19W80PS(via DVI), and a Sylvania LC195SL9 A LCD TV(via HDMI).
The stock resolution of the TV is 1440x900. If I run it at that, the display area is much larger than the screen. I have to manually change the display to 1280x800 for it to be even closely correct, although the image is distorted slightly(stretched vertically).
I make the changes using (3) xrand commands:
xrandr --newmode 1280x800 85.25 1368 1440 1576 1784 768 771 781 798 -hsync +vsync
xrandr --addmode HDMI-0 1280x800
xrandr --output HDMI-0 --mode 1280x800
I have to do this every time I start the computer.
I attempted to add the commands to the rc.local file as root. The result wasn't as expected. When I booted the system the screen resolution was changed to 640x480.