The Impact of Gender Composition on Team Performance and Decision-Making: Evidence from the Field
http://www.econ.upf.edu/~apesteguia/Gender_Teams.pdf
"Looking across the performance distribution, we find that for undergraduates, three women teams are
outperformed throughout... For MBA students, at the
top, the best performing group is two men and one woman."
http://hbr.org/2011/06/defend-your-research-what-makes-a-tea...
"The standard argument is that diversity is good and you should have both men and women in a group. But so far, the data show, the more women, the better."
http://www.20-first.com/968-0-lbs-study-shows-addition-of-wo...
"The optimal percentage for the gender balance of men and women on teams is 50:50.
Neither men nor women flourish when in a minority on teams. When in a minority, women tend to network outside whereas men tend to become less motivated.
Having a slight majority of women on teams (about 60%) improves the self-confidence of the team."
I think the evidence is pretty clear. Anecdotally, I've seen the best performance out of mixed teams. All men teams and all women teams generally don't work out so well.