"In general on the internet it's safe to assume that a fair number of people claiming to be female are actually men or teenage boys, so this would suggest that only a tiny proportion of Wikipedians are genuine ladies."
I'd argue that the opposite probably applies to Wikipedia. There's little to no advantage to be a male pretending to be female on Wikipedia, in fact, the popular perception that females have less input there would even work against it. There are probably a fair number of female masquerading as men there.
Instead of looking at what gender Wikipedia users identify at, it would be much more instructive to isolate ways women and men compose their language (yes, there are differences), and put some algorithms together to see how that runs across Wikipedia articles in general. I suspect the results would be a lot more even.