I haven't capped genders but I can see how you might have to, depending on the sort of game it is. I have capped good guys when we had an influx of them as it was affecting the dynamic in terms of wider plot. Generally I'd always do the whole most wanted/least wanted thing first, unless the imbalance happened really suddenly. I think the point at which I'd cap is if it felt like it was really interfering with the dynamic of the game.