In case it's of any use in the future, there are several converters around, many with file splitting based on size, and some that do batches, but in my opinion Avisynth would probably produce the best, quickest result. The caveat: it can get complicated because of the sheer volume of plug-ins & functions available and their settings -- if interested it's often best to post and ask in the avisynth forum.
A *very simple* use would be to write the script using Directshowsource I think with the wmv filename, opening that in VirtualDub, selecting fast recompress & your new desired final codec, then saving a segmented avi. V/Dub handles some batch processing. The advantage is that the image will be decoded using MS software, as it would be used in wmplayer, but kept as much as possible in it's original format & presented to the new codec that way -- it's both fast and very accurate, used by enthusiasts and pros worldwide.
Avisynth.org with forums on doom9.org