My main aim is brilliant, sharp photo quality. I dont care about video or fps. I just want the sharpest, clearest quality pictures to print A0 and larger. Which camera is the best - the EOS 5D III with its 22.3 MP or the 1D-X which has less MP but the Dual Imahe Processor? Any advice?
Dual image processors are all about speed, the software that delivers quality will just run faster if there are dual processors. To get the best out of either quality, you will need a high quality lens.
The 1D X is a bigger heavier, faster body. The 5D Mk III is slower but makes slightly larger files.
5D Mk III: 5760 X 3840
1D X : 5184 X 3456
There is not really enough difference in file size to be a factor, less than 600 pixels of width and less than 400 pixels of height. I doubt there will be much difference in the image quality, either. The major considerations are speed, dual memory cards and cost.
As always my recommendation is to try it out in the store using your own cards, then look at the results on your computer before making up your mind.
Early look at 5D Mk III: http://www.digitalrev.com/article/canon-5d-mark-iii-hands/MTA3ODU3M...