Paul,
The images are interesting, and so is the EXIF data ...
car1.jpg -- EOS 1DsMkIII, ISO 100, 1/250, f/11
car2.jpg -- EOS 1DMkIII, ISO 400, 1/3200, f/4.5
Given that it was "awful, bright sun", did you intentionally overexpose the second image by a stop, or are your cameras' meters really that different?
Robert
PS I notice the 1DsMkIII shot has been given +0.55 Exposure in ACR post-processing. Curiouser and curiouser. ;-)