This is my setting for PAL Low-Res 320x256 (needed for games, demos etc.)
I had to set up a new VGA mode which enables me to use a 640x512 resolution at a lower clock (values may vary; I tested clock rates between 35-40 and they all worked fine). The picture doesn't fit 100%. Testing a few games, I noticed that one or two pixels on the left and right edge are cropped away. No fatal loss in the end. Maybe this will be fixed/optimized in later versions.