Naughty Marek!
Now look what you've done! Instant thread derailment.
Ah well, here goes - "Chair" is the oldest form, according to online etymological dictionary, and "Chairwoman" dates back nearly as far as "Chairman", and both those are from the 17th century.
Delightful though men are, I would still nevertheless be miffed were I to be called "Chairman". I'm not a man.
An answer is personal preference. If a woman wants to be called "Chairman" instead pf "Chairwoman" (or couldn't care less what she's called, as long as she's in charge!) then that's fine. If a man wants to be called "Chairwoman" instead of "Chairman" then that's fine too.
Madam Mayor, anyone?
And, in an attempt to get back on track, I don't think I'll ever be congratulating Nigel on achieving that one ...