I tried to shutdown gdm (/etc/init.d gdm3 stop) and then run Xorg -configure. It gave me a xorg.conf, but it didn't work as you mentioned it could've.
I tried to change/add/remove some settings, and googled around for solutions still without luck. I managed to get the Gnome manager to stop showing the '1156x???' resolution. Now, however, it added '1366x768'.
I have _no_ idea why it did that.
Then I found a much simpler xorg.conf sample on google, and after adding the 1280x1024 modeline and the 1280x1024 mode i went to try it, and now it only shows 1 resolution - 1024x768?? That resolution isn't even in the xorg.config??
a) Matrox MGA G200e onboard VGA gfx
b) It seems like it does. in the xorg.conf that Xorg -configure generated, it also listed the graphicscard.
c) i think it's defaulting to 1024x768.
I uploaded my log and my xorg.conf - maybe you can see what i did wrong?
Notice how brilliantly my domain matches my situation :-)