This all "how much cpu" is almost nonsense to me

-I recommend to use default media-player or kmplayer with default media-player streamer
-Use handbrake settings that have been given in link maemo.org wiki and this way you should get video encoded in correct codecs (video&audio) with correct settings and container that gets HW-acceleration on N900.

If you still se stuttering then lower bitrate.

From here yous hould get HQ trailers that have been encoded on quality that should still give you stutter free playback. But what I have tested these clips are on "edge" of performance capability of N900:
http://talk.maemo.org/showthread.php?t=39034