Using 4-bit .gif improved the filesize of the final ebook a lot. The .imp now is 50 MB, .epub now 43 MB and .prc (stnd) is 44 MB & .prc (high compression) is 37 MB. There was very little image quality loss reducing from 16M colors to 16 colors.
Still too big to be useful.
If I exclude images, then the resulting filesizes are: 23 MB .imp, 14 MB .epub and 16 MB .prc (stnd).

much more useable...
I'll experiment a bit more and see if using the Wikipedia 2006 CD source directly instead of the plucker extracted .html/images works just as good or better.
Stay tuned...