I suppose you'd classify me (though I dislike classification) as more of a masochist than a pain slut. I remember there was a thread somewhere about "good" pain and "bad" pain, and I'm reminded of it at the moment. For me, not all pain is good (stubbing my toe on the coffee table hurts like a *&Y@!) but sometimes when mundane things that hurt *can* feel good (Last night, for example, I cut my hand fixing dinner...yeah, it hurt, but after that first "ouch!", it was a "good" hurt, but then again I like watching myself bleed.)
As far as having requirements for "my" sadists...I'll put it this way. I know I can't be happy being a submissive without being a masochist. (If he doesn't *want* to hurt me, then on some level, I never feel completely fulfilled.) That desire to inflict pain has to come from him...if he's just doing it because it turns me on, it still isn't enough. I'm constantly learning, looking for new ways to push my pain threshold.
It's also interesting to note that it takes a lot for me to make myself hurt--I don't know if I'm anticipating it in my head or what--but the "ouch!" factor of self-punishment is never as great as it is if it's someone else's hand holding the whip, so to speak. Does that make sense?
I know I'm rambling and much of this is highly subjective. It's only my personal point of view/opinions, so feel free to comment or disregard as you see fit.