Came across this post in which the "boxing" photos were taken with a 645D and two Pentax 645 prime lenses:-
http://www.dchome.net/viewthread.php?tid=997822&extra=page%3D1
(in Chinese, Google Translation in English Here)
Most of the photos are really nice and I like the above two most. But in fact, they are actually still photos taken with a studio setup lit by studio bulbs. The girl is not a real boxer but just a model. So, I think we have to wait next time for real world sport photos made by the 645D, if there will be any! I hope that the camera and system would be fast enough~ ;-)