Biologically women have faster reflexes and some would say a higher pain threshold than men
Huh? I've never heard that. In fact, the only study I could find on the matter found the
reverse to be true, and that (despite what kitsch pseudo-science shows like Mythbusters claim) women experience
greater pain than men.
See, this is a big part of the problem I usually find with female characters: the author usually appears to be so laboured by the desire to create an inoffensive female character that s/he creates a completely unbelievable female character that plays out more like Zeus than a real woman.
I totally agree with Sabolich; I think that, by far, the most interesting female characters are those that are three dimensional, rather than a mere "Yeah! Girl power!" derivative. I'm not put off by female characters per se, but it's just that I know that most of the time the female character will be offensively boring with the exact same 'inexplicably hates men and inexplicably kicks their behinds' theme I've seen a bazillion times.
As regards the OP, I don't know whether women are under represented in modern fantasy. I know that GRRM has some cracking female characters that respond coherently to both their internal desires and their societal constraints (Arya, Catelyn etc).
But, honestly, I'm fine with anything that can suspend my disbelief and present me with something novel; it's just that far too many female characters (that aren't just the meek type) fail on both those counts.
EDIT:
I know men are stronger than women, but I'm a (UK) size 6 and 5'4. I'm pretty weedy and yet I did karate for several years and was perfectly capable of throwing a man over my shoulder (yes, I have done it). It's all about using your opponent's size/strength against them. So... yeah. Just cos (some) women aren't as strong, doesn't mean they can't kick a man's ass. Should've seen the looks on some of the guys' faces when I punched them and it actually hurt.
Granted, Mouse, women
can train to use their opponents' strengths against them, but there's a
big difference between a woman hitting a man who (due to modern societal constraints) can't hit her back, and a woman hitting a man who can go all out on her. Unless the female character is much better talented, armed, or trained than the male combatant, it's just hard to see an outcome where two equally talented, armed, and trained combatants of opposite genders would have any unpredictable outcomes.
To put it in perspective, a US military cross-gender study
found that
male soldiers’ strength relative to females as follows: upper-body, 72 percent higher; leg extensor, 54 percent; trunk flexor, 47 percent; lean body mass, 33 percent; and aerobic capacity, 28 percent.
That's
a lot of extra muscle, and given that human muscles put out almost six lbs per square inch (gah, this is starting to feel a lot like my biology lectures again), you're looking at hundreds, if not thousands, of pounds of strength difference.
This is why it's so important to make it crystal clear why a female character is able to beat a male character in combat. It becomes so perilous that, in my opinion, it's better to just avoid the issue wherever possible, and permit women to play to their actual strengths in a medieval setting: men will never see them coming.
That's not to say that a world
can't be created where women can beat men (it's your novel, so you set the darn rules!), but it's just going to be tough to do so without seriously smashing against the readers' known rules about reality.