For some reason, my monitor won't show anything at the VGA preset (640x480 60 Hz). It acts like there is no signal at all.
Since my monitor also supports 75 Hz input, I decided to give it a try, also to see if it would improve scrolling smoothness. It wouldn't give me any picture at low pixel clocks, but by going up I did make a 640x480 setting at 75 Hz which seemed to work well.
By using this for PAL, it will cut off a little bit in the bottom, but few games use this area anyway, so it might be a good compromise if you want a full screen. On the Superfrog pic you can see that a bit of the text has been cut off and likewise on the AmigaDOS screenie.
Edit: Oh, and it didn't improve scrolling on my monitor, but I have a suspicion that it might resample back to 60 Hz before refeshing the panel, which is why it looks more fluid in plain 60 Hz mode. On a CRT, it should look better though.