When writing/reading historical fiction I generally go by how long the participants have been dead. I tend to feel better about it if they and their immediate family are all deceased. Of course, as I've noticed once or twice, there are still people out there capable of taking deep and personal offense at a non-vanilla portrayal of a long-dead historical figure (aka the infamous "Okita wasn't gay, he murdered people!" debacle) but let's face it, those people need lives!

You raise a very interesting point, though, regarding RPF writing about characters who have been more "officially" RPF'd before. Especially when it is, as it were, second-hand. Take the Musketeer fandom, for example - I feel guiltless when writing about d'Artagnan even though he was a historical figure, because the person I'm slashing with Athos ficcing is filtered, in a manner of speaking, through Dumas and Courtilz before him and probably has very little resemblance to the actual Charles Castelmore d'Artagnan.

This argument becomes uncomfortable, though, because it can be argued that the outward persona of an actor doesn't necessarily bear much resemblance to that actor's real self either... which means actor-fic could be justified. And what about, say, those Japanese boy-bands who flirt and carry on with each other on stage as part of their show, more or less?

Which is what bothers me, because in practice I'm uncomfortable with actor-fic to the point where I find it hard to write anything but the blandest sort of genfic for any movie or TV series. Thank god for anime (and text).