I made an attempt to shoot video at a small oval race track last week, it was my first time shooting video with the 5D Mk III (or much of anything else for that matter). I'm disappointed with the results. Because of the speed of the cars I thought shooting at 60 fps would be a wise choice for better slow motion of the inevitable accidents. This meant 720p. The video is very soft, I've read since that some consider 720 to be unusable.
My setup was: 24-70 @ 70mm w/ f4-f8 (changed as the sun went down), 720 @ 60 IPB (>4 hours of shooting so space issues, don't want to change cards in the middle of a race), ISO 500 - 12800 (again, changed as the sun went down, poorly lit track) Tripod was used (paned with the cars), Zoom H4n (audio is fine).
Would 1080p 30 be a better choice with the trade off of slow motion? And perhaps a shutter of 125 or higher for a sharper look?
Most of the action happens at > 150 ft from the camera, the closest I get to the cars is ~50 feet.