I think Requiem has so far the biggest chances for international distribution, considering the awards and attention it got, and the (popular?) topic of exorcism (with which it actually deals only marginally).
I'm extremely fond of Possession, as it is imo one of the best depictions of traumatic relationships on screen. I especially love it how it depicts a totally altered perception of the world under extreme psychological strain. Very honest and true to life without merely replicating it, but adding a complete reflective process.
As for Requiem, there can't be any real comparison besides some very short acting scenes. Schmid seems to be nowhere the director Zulawski was, as he is imo far better with observing inner depictions in an "impressionistic" way, than with exposing them outwardly like Zulawski - a completely different approach to film.
And Requiem has many problems with dialogue and character-confrontation when it doesn't rise over regular TV-fare in many moments (luckily, compared to most TV, the acting is far better!).

I'll keep you informed on a DVD release that will at least surely be available here in Germany. But as of now, I have no information, otherwise I would have posted a link. Seems like some good habits are rubbing off on me