I only like
Michael on girls (like the character from
Star Trek.)
I don't like
Gaius but I do like
Gaia*;
Alanis but not
Alan;
Edwin but not
Edwina;
Angel (on any gender) but not
Angela;
Phillipa but not
Phillip;
August but not
Augusta.
As far as I can tell, it's mostly a stress-placement thing - excepting
Gaius vs
Gaia, which is because of their associations.
*Most of the time,
Gaia is unrelated to
Gaius, but there is some evidence that it was occasionally used as a feminine form in an oath that was recited during wedding ceremonies ("Where you are
Gaius, I will be
Gaia..."). I don't know if it was used in that on any real people, though.