idk about Jeff, but it seems to be a 30 KB xml file that when I open up using management studio, just brings up a blank page. I do have one question however: have you tested several times for consistency ? Just to make absolutely certain that the behavior is consistent(Read committed always results in faster exec time) ?

Cant understand how that could be the case. Read uncommitted should have(if anything) lesser overhead because of the locks. Cant understand why there would be a difference in the execution plans at all.