The best way to keep the size down while retaining reasonable picture quality is to use XviD in 2-pass mode.  You can typically use half the bitrate of a single pass and get about the same quality.

Unfortunately, I can't tell whether SUPER supports 2-pass or not. It would be hard to imagine an encoding app that doesn't, but there's no mention of it in the FAQ, as I would expect, and the forum doesn't appear to be searchable for some reason, without which finding an answer to a question like that would take impossibly long. Usually this function is obtained by manipulating the codec itself.  SUPER doesn't  seem to have this feature, unless it's what the "High Quality" tickbox does.  The FAQ doesn't mention that, either.