I know this is a stereotype but it seems that women have less of an "I need to prove myself" instinct than men, atleast were Aikido is concerned. So theoretically you can go even harder and faster with the girls before they see it as a personal attack and their egos start suffering than you can with the boys.
Also girls smell nicer and are prettier to look at.
![Big Grin](images/smilies/biggrin.gif)