I agree that the capacity for a person to do harm is not necessarily based on their size or gender. I think it has more to do with their own intentions-- what kind of violence it is. In my own experience with a BPD male (who was much larger and stronger than I), he was more often violent to himself (punching himself in the face, punching brick walls until his knuckles bled, and then saying it was my fault, etc...), then he was violent to me. When he did hurt me it was not in order to cause me serious physical pain so much as to scare me. Often he did it when, during some ridiculous argument, I would get fed up and tell him I was going home. His abandonment anxieties would provoke him to run after me and slam me against a wall or slam me onto the floor, so as to prevent me from leaving his apartment. He did however, injure me quite seriously on one of these occasions. And of course, emotionally I was traumatized, was later told by my therapist I was probably suffering from PTSD.
That being said, I think that while he did not usually cause me real physical injury during his rages, the knowledge that he was so much larger than me made me absolutely terrified of what he MIGHT do, and I imagine this size imbalance might often make the plight of the woman dealing with a male BPD more difficult than vice-versa. My ex-BPD was often totally out of control, and there is no way I could have defended myself against him, had he really wanted to hurt me. After we'd gotten back together following a 6-week breakup, he managed not to be violent to me for a couple months (but was still prone to punching himself and saying it was my fault). The first time he resumed physical aggression to me, I left him for good. We only were together for only a year, so who knows how bad the violence could have gotten. (And, in the spirit of honesty, I should confess that I slapped his face on three occasions, albeit rather weakly.)