I find the competition aspect interesting. The closest I've ever come with is the opposite. When I had discussions with friends about what we'd do if guys cheated on us, I always thought, if it's with a guy it won't be as bad, because I would get it, that the guy gives him things I can't. But with another woman I thought I might feel like I was being judged against her and compared, etc.
That was way before I thought about being with a poly person though. Now it really doesn't matter if their partners are male or female, I'm not going to feel like there is competition of any kind. Cheating would be even worse though, because it would be hurting me for the sake of hurting me.
About polysexual, I've head people, in that context, that "monosexual" for someone who is either gay or straight, and "polysexual" for someone who is bi or pan. However, in a polyamorous contexts, these words are also used to mean someone who has sex with several people or just one, respectively, which I think makes the whole thing confusing.