Help displaying to 1680x1050 monitor on laptop external VGA port

[Brandon Kuczenski]

Hi,

I'm working on getting a Samsung Syncmaster T220 LCD to display its native 
resolution of 1680x1050 px on the external VGA port of an x200 laptop. 
The hardware is an Intel GM45 express chipset with integrated graphics.

The display works fine on a desktop machine running debian and 
xserver-xorg 7.1.0-19 using the VESA standard mode setting:

"1680x1050"  147.14  1680 1784 1968 2256  1050 1051 1054 1087

The mode is specified in xorg.conf and everything is happy.

The laptop runs xserver-xorg 1:7.4~5ubuntu18 and doesn't use xorg.conf. 
I rely on gnome-display-properties and xrandr to adjust display settings. 
[which I hate-- after 7 years I finally started to understand xorg.conf 
well enough to monkey with it] X does not offer the 1680x1050 mode, so I 
have to add it with xrandr.

When I use the same modeline on the laptop, the display shows aliasing 
effects at hard edges and leaves a black bar at the right edge of the 
screen (about 100 px wide).  If I add +hsync -vsync (per monitor specs) 
then the image gets squashed into a roughly 4x3 aspect ratio.  I can't 
seem to come up with any settings that display properly at the native 
resolution.  The laptop doesn't have a DVI port; otherwise I'd use that.

Am I to infer that the laptop hardware cannot display that resolution?  I 
haven't found any clear authoritative statement of hardware capabilities 
for the GM45 chipset displaying to the external VGA port. At this point I 
don't know whether the failure is in xorg, ubuntu modifications, laptop 
hardware or a finicky monitor.  I'd appreciate any pointers or 
suggestions.

Thanks in advance,
Brandon