Anasazie, I don't think Kinski's portrayal was necessarily "just a performance." If anything, I'd consider it more of a non-performance. The beauty of his portrayal is that he slowly ascends into the foreground after a fairly secondary role in the earlier scenes. His monologues towards the end of the film are what ultimately give his performance, and the film, power.
I do think that the better the film is, the more a director can get from an actor, mainly because most great films have characters that are deep, ambiguous, and easily related to real life people. That's why I hate that Robert DeNiro never really worked with genius directors, he followed Scorsese his whole career. He's amazing in Once Upon a Time in America though.
With that said, good call on Alain Delon in Le Samourai. He almost never breaks his driven intensity, aside the scene in the car towards the end, which just shows how skilled he is. That'd probably be my second choice next to Kinski, along with Michael Pitt in Last Days.
Thanks for the insight.