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I know of a fellow timelapse shooter who uses 5D Mark II, named Randy Halverson (dakotalapse.com). He seems pretty open about what he's doing so you might ask him a question or two. He obviously likes the camera, or wouldn't have upgrade to it in the last year or so.
Of course timelapses aren't traditional video in origin, but rather hundreds of stills stitched together. This seems a very popular approach these days to get really high quality footage, and to do night sequences.