I really curious too. In the past I made some internet researches but
didn't find anything satisfying. So I hope someone can find some reliable
statistics.
Anyway, I could find just these two pages (of the same author):
http://shogi.typepad.jp/eweblog/2009/06/winning-percent.html
https://groups.google.com/forum/?fromgroups=#!topic/shogi-l/GixqTlUmSpI