Here is the definition of dynamic range:
http://learn.hamamatsu.com/articles/dynamicrange.html
Full Well depth is usually simply a function of the size of the pixel (there may be other considerations but that is what I know). 5D iii pixels are slightly smaller than Mark ii. (
http://www.ptgrey.com/support/kb/index.asp?a=4&q=192 unless Canon lowered the voltage).
So assuming full wells are smaller then the only way noise is lower is if dynamic range was also larger than the mark ii - right?
Unless they managed to increase full well depth by reducing voltages.
Well per one poster on DPReview, dynamic range for the mark iii is slightly lower than for the mark ii.
So how could ISO performance in the mark iii be improved over the mark ii without some trickery (like RAWs are being smoothed first - mind you Nikon does that).
Greg.