Someone on-line posted a graph of the noise vs. ISO settings for the 5D Mark III.
I have decided what I am going to do is to make myself a bunch of different profiles for all the ISO values I normally use based on the noise figures from this graph.
While the information in this graph may not be exactly the same for my 5D Mark III, I am sure it is more accurate than I could get by doing tests with my camera.
This way, all my images are corrected for noise as they are being imported into my computer.