Ill say this. My i7 920 has plex installed. I store on my unraid server. I stream plex to my ps3 and have 20mb bitrate movies that stream perfectly with no hiccups at all.
I7 920, stock clock,asus p6x58d-p.
So keep in mind im able to stream with that setup beautifully. You dont always need new cpu architecture to play these movies.