Uh, I'd rank the 8400 in first as the best overall performer. I don't want to make a list, since I didn't compare them all directly. Of the ones I've listed I only own the Germans, Quarts, 272's and 8400's at the moment.. I want to get rid of all I can. Some strange qualities about the 8.35's on which I can't quite put my finger. Just listened to some music with vocals (I'm starting to understand why people evaluate headphones with vocals) and when a certain woman sang note to note along a trumpet, the 8.35D couldn't grasp it, for instance. K272's would probably be second, or the GMP's, not sure. The AKG's are very easy to listen (and follow) but don't extend so well, leaving some harmonics either subdued or completely silent. Still, very good articulation across spectrum and probably the best balanced. Though again, the KRK makes many musical cues much more apparent and easier to listen (or monitor), were it bass notes, drummer's cymbals or brass timbre. Mmm.
Haven't heard the K550 yet. I'd like to.