Gender differences are a hot-button topic, so I'll make this clear:
Actually causing stats or skills to be better or worse based on Gender isn't actually realistic. The primary (and often only) difference between a man and a woman attempting something is not the efficiency of a tasks completion or how well it was done, but the method that makes that task easiest to them. There are even real world exceptions to this rule of thumb, and most of the females that could be considered exceptions are the type of woman you'd expect to be adventuring in the first place.
Ultimately, this seems like the only proper way to add a guide to these differences:
1: The GM would be advised that forcing player characters to use the data provided would be both unrealistic and extremely prone to splitting the group at the seams.
2: Data provided would be non-mechanical, and focus on strengths of each gender rather than weaknesses, as well as pointing out the utility of each "Strength" in a manner that shows no preference for either. If Data on this would reinforce any negative stereotype, it is omitted for the sake of preventing problems.
3: Each strength pointed out should result in, at most, a "preferred" or "New" way to use the skill it effects. Example: A focus on Upper Body Strength (Men) or Lower Body Strength (Women), differences in how each gender solves the same problems logically with similar effectiveness, and Stunts that rely on the strengths common to that gender (Spot Details for women, Notice in Low Light for men). The utility of these should be equivalent to that of their counterpart of the opposite gender.
4: This should go without saying, but pointing out strengths that paint a negative picture of either gender isn't a good idea. For example, you shouldn't have a female character with the specialization in "Streetwise" of "Gossip", because it paints a very negative picture of women, just the same as a man shouldn't have a "Stealth" specialization for "Peeping Tom" for the same reason. Obviously, depending on background this could be waived, but the source of these should NEVER be just the gender of the character, and the group needs to be okay with a character with these flaws as focuses for skills. If the group's majority votes no (with the GM's vote counted a second time if a tie happens), this is a perfectly good reason for you being ejected from that group, especially if you've already been warned about it.
5: I shouldn't have to say this, but SHOW YOUR WORK. Any research that points to the advantages of either gender in a certain way should be mentioned with other research materials in a bibliography at the back of the book, that has an entry in the table of contents. It's a lot easier to justify adding gender differences even as an optional rule if you have research you can point to from credible sources that confirms the differences in the system. Likewise, emphasize that these rules are not "Hardwired" into the game, and can be ignored if they would cause arguments... And once again, that the GM shouldn't force players to use any of the suggestions offered, but depending on the group may have the right to forbid use of the suggestions given on the basis of gender alone.
My Rationale is:
1: Men and women are largely capable of the same accomplishments given the proper training and opportunity; However, scientific data suggests that due to the differences between men and women (both body and mind) it is often easier easier to be good at a task using different methods of accomplishing it by each gender for the majority of either. I say "Majority" because there are exceptions in real life too, and while not extremely common, they are more common than you think (Also, the most likely to act contrary to traditional roles, which is why most female adventurers aren't normal according to the society which they came from).
2: By focusing on the strengths of each AND making including them all optional, suggested skill foci that affect the method (rather than the effectiveness) of skill uses in ways equivalent in utility and accessibility, You are avoiding painting any single gender as "superior" or "inferior" to it's counterpart.
3: By not mentioning perceived or believed strengths that violate religious or secular morality to either gender on sole basis of that gender, you avoid validating negative stereotypes about that gender. By not touching the stats or skills themselves beyond suggesting a single focus for them (Taken out of the number able to be chosen normally), you are reinforcing the idea of "Different Yet Equal" that is key to dismantling prejudice of any kind (though in this instance, it's sexism in particular)
4A: The above three principles allow for strong female characters that aren't evocative of tomboys specifically, but reinforce the ability of a properly written female protagonist of any profession in particular to be both strong AND feminine, without resorting to making them "Men at heart" (One of the few ways strong female characters are portrayed in Hollywood, the other being as a villain or with partial nudity). The fact they're optional allows players to make the kind of exceptions to societal roles and physiological traits that do exist in the real world among females. And the fact that EACH element is optional means you can pick exactly where on the spectrum of masculine/feminine nature a female character falls in method and behavior without forcing penalties on the character.
4B: Likewise, principles 1-3 allow the creation of sensitive male heroes without forcing them to mirror negative stereotypes about such things, while allowing the "masculine and tough" males common in fiction and present in real life to be properly represented as well. Again, this also allows you to pick where on the "Masculine/Feminine" spectrum of behavior and modus operendi any male character falls into without forcing penalties to be applied to the character.
5: By not tying stats to gender at all, quite a few other problems are avoided entirely, leaving it much easier to explain the differences without showing prejudice that may or may not exist within you. By not reducing skills, you likewise are avoiding "Go Back to the Kitchen" syndrome.
6: By not outright suggesting foci for specific skills, but instead giving the information to the player without tying it to any direct mechanical choice at character creation, the player will fill in the blanks themselves, creating a greater diversity of characters of both genders.