A big difference
A reader sent in a quick comparison between the Canon EOS-1D X and Canon EOS 5D Mark III showing a very different color rendition as well as a significant difference in noise performance at ISO 25,600.
The Quick Test
The following test was conducted at sunset. This is the reason for the white balance setting, which on my 5d3 most closely approximated the warm tone of the light. Both files were dialed in at 8000k, +15 magenta. Both use the exact same lens, and were shot within 1 minute of each other. Both files are DNG 7.1, process version PV2012, and use the camera calibration setting “Camera Neutral.” All other settings including sharpening, noise reduction, tone curve, etc are all zero’d out for consistency. I’m using the latest version of Adobe Photoshop Lightroom available as of this writing, which is 4.1.