I would say the major diff

I would say the major difference is depth of field. the 5D will give you shallower DoF than the EX3. If you want shallower DoF, then go with the 5D.

The 5D MkIII allows you to output through HDMI, so you can actually get less compressed video than previous generations. But the EX3 allows you to output via HD-SDI, so you can get really nice video from that connection as well.

So I think it comes down to the look you hope to achieve: shallow DoF vs deep DoF.