I took the following
210147 a.tif
and did:

mogrify -scale 600x1200 -format jpeg *.tif
34815 a.jpeg.0
51699 a.jpeg.1
56333 a.jpeg.2
56718 a.jpeg.3

This cut the picture down to less than
1/4 the original size, and seems the limit
on viewable.

Which means I only save about 20%.

Can I do any better?