if it was me.... I would get the 600D, the kit lens is definitely adequate and the articulating LCD screen on the 600d is a god send if you dont have a field monitor
75-300 wont get much use in filmmaking..
here let me save you $200 ... buy today!
http://www.frys.com/product/6176789?ref=Cheesycam.com
oh wait, might be in store only..