Of course, what's most important is photo quality and here is where the Mark III really pushes ahead of the Mark II.
There really isn't any difference in detail between the 21-megapixel Mark II and the 22-megapixel Mark III, at least at lower ISO settings. Coupled with a good lens, both cameras exhibited loads of detail.
If anything, the Mark III's metering system was slightly better at coping with extreme lighting conditions.
White balance is markedly improved in the Mark III - we took a few interior shots using tungsten lighting with both cameras, and the Mark III proved much better at getting the white balance right.
The biggest noticeable difference, however, is that the Mark III is a lot better at high ISO settings than the Mark II.
While detail and noise are much the same between the two cameras up to ISO 800 or so, by ISO 1,600, the Mark III is still producing clean, nearly noise-free images while the Mark II is starting to show some noise in shadow areas.
By ISO 3,200, the Mark III pulls comfortably ahead, producing still relatively clean and usable images with only a hint of noise while the Mark II is already showing quite a bit of noise.
On the Mark III, noise is still well controlled at ISO 6,400 and produces images which has only a slight loss of detail, but which I would still not hesitate to use if I needed to.
ISO 12,800 is at the limit of what's acceptable to our eyes - there is a noticeable loss of detail, but even here, noise is very well controlled.
By the time you crank up ISO to 25,600, noise reduction kicks in quite hard and you start losing a lot of detail and colour saturation also starts to suffer.
Overall, top marks for image quality and noise control.
As with all modern cameras, the 5D Mark III has very good battery life and certainly nothing to complain about.
For those interested, you can download the full-resolution photos from our Picasa site at goo.gl/photos/oTaHZikqxF.
Remember to go to Actions then Download Photo to download the whole file if you want to evaluate quality.