If you could get me an X bin Luxeon III, I would be a very happy man!
As of now, the brightest 1w is an R bin, brightest 3w is a T bin and brightest 5w is an X bin. There have been a rare sighting of a single S bin 1w and a U bin Luxeon III.
Now, if you want to get an X bin 5 watter...and you get one, let the rest of us know!