Anyway, could 1080p playback from an mkv file (let's leave aside the BR thing) be possible with the fastest G4 cards?

In my 1.25Ghz G4, 1080p is not so slow... I should make deeper analysis, but I'd say I got around 18fps, and around whole 25fps with low-bitrate parts (very darks scenes, and all that).

Could anyone with a 1.8Ghz sonnet card try 1080p mkv reproduction in mplayer? It might be enough... I don't know...