I scan at 400dpi 1bpp and save the pages using group4 compressed TIFFs
which is the maximum res the IS520 scans at.
Acrobat does a really poor job of saving JPEGs (it makes them a LOT
bigger than the originals) and I would NOT use a lossy format on any
page with only text or line art. There is a noticable loss of edge
contrast on text pages compressed as JPEGs.