just wanted to sugest some other data prefilter processor

WRT whivh is a text prefilter
http://www.ii.uni.wroc.pl/~inikep/research/WRT41.zip

it works by replacing common english word from a dictionary into some codes. it really helps compression

there are more dictionaries for other langues then english here
http://www.ii.uni.wroc.pl/~inikep/research/

the filter+ppmd compression on text files would be nice.