Just a quick video I shot to compare images from the cameras. Footage from both converted to Apple Pro Res 422. Let me say up front that this test is not scientific in any sense or meant to imply this, it is simply a comparison of the footage I was able to capture from the cameras on this day.
Settings identical except where noted a difference in Picture Profiles. No color grading was done though there is a slight difference in some shots due to using an ND filter to achieve proper exposure (I was wrestling with gloomy to sunny skies at times). Lens used for side by sides was Canon's 24-70 2.8 L and low light test done using Canon 35mm 1.4L
Sharpening in final 3 shots done directly in FCP by adding the Sharpening Effect. Though there is only slight improvement in the image quality directly from the 5D mark lll there is definitely more room to work with the footage in post with sharpening and color grading. Low light shots is where these two cameras are truly different. The dynamic range of the mark lll is an incredible improvement.
There are more tests to come and also my written review of the experience at twolightfims.com