Both monitors can only display the TV modes (PAL and NTSC). VGA modes as created by a scandoubler cannot be displayed. I don't know anything about the quality of both monitors but regarding the available resolutions there is no difference. You should be able to get 640x512 with interlace, though. You should even be able to get 1280x512 (PAL:Super Hires Interlaced) although it's probably not readable at all.
Bye,
Thomas