Hi Sarah. I've had several same-sex dogs, male and female, that have lived in perfect harmony (well, by that I really mean relative harmony!)!
I think you're right though when you say it's as much a personality thing as it is a gender thing. If it "feels" like their personalities will work, they probably will!
I don't at all subscribe to the perspective that suggests that once females fight they can never get over it...I've seen it happen too many times. Even with animosity, 2 bitches can be as bitchy as they want and still get along reasonably well.
My current female and another female that lives here got into a spat once, and there has been some strutting and posturing around each other since, but no further violence between them...
A lot of how it goes is on you though! If you are tense when they get tense (if they ever do), they will pick up on that.
It's not the size of the dog in the fight, it's the size of the fight in the dog. Mark Twain