I have used both the 5D and Canon’s XF305. The advantages of the 5D is lens choices and that shallow depth of field people seem to be in love with. However, I also have to record audio to an ancillary device like a Zoom H4v. Even with audio tools like Plural Eyes, on a long shoot, re-syncing all that audio is a PITA. The problem with the shallow depth of field is the subject focus is problematic when doing hand-held work; it is a difficult rig to manage off a tripod. The 5D is a remarkable still camera – likely one of the best.
The Canon XF305 (similar to the EX1) is a superior video imaging device, with up to 50 Mbps recording capability in a 4:2:2 color space. For green screen work this is essential. AND, XLR inputs for discrete balanced audio synced to the picture ! Each device has its benefits but for serious video acquisition, I would always prefer the camera designed for video, not a still camera which can record video.
Jerry Newton