"Should I just go ahead and change XFreeConfig?"
You could try 1280 x 800 and see how it works. If it does not work then X Window may not work. So make sure that you can get to a command line if X Window fails and make sure that you have a command line editor available so that you can change XFreeConfig back to 1280 x 1024 if necessary.
Be prepared. Create a LifeBoat CD.