Andy: I am sure you may have taken care of this, but I'd still like to clarify something about the 75% quality setting. As far as I know, there is no quantitative concensus about what 75% really means. In fact, 75% on Paint Shop Pro equals 25% on the IJG scale, so I would just like to verify which software you are using to determine the quality.
Since equinox's 60K (lossless compressed) file went to 15K (lossy compressed), I would assume that you are using something similar to 75% on the IJG scale. Also, if possible, JPEG2000 will probably be better than JPEG at reducing the bit rate with a more graceful degradation in picture quality.