Didn't see this in the other thread, what happens when you type
It should show the 1680x1050 mode under your HDMI connector, but it might not be under the VGA connector. You probably just need to add the correct mode to your xorg.conf file, but I hate editing that.
xrandr --addmode VGA 1680x1050
xrandr --output VGA --mode 1680x1050
where VGA might be VGA0 and 1680x1050 might have additional characters for refresh rate, etc.