OK, well your /etc/X11/xorg.conf seems to be missing some stuff. I would suggest adding;
While you're at it, get rid of all those " ### Comment all HorizSync and VertSync values to use DDC:" lines ;-)
In your 'Section "Screen"', 'SubSection "Display"', you need to add the 1600x1200 mode.
I haven't been able to track down the frequency specs for your monitor, so I'm assuming for now that the figures you have are correct.
Try adding 'Option "UseEDID" "False" in your Screen section. You can look up the various different option at http://us.download.nvidia.com/XFree8...ppendix-d.html
Hope that helps a bit.