Just published in my review of the Canon 5D Mark III in DAP is another comparison from ISO 50 to ISO 25600 versus the 5D Mark II at whole ISO values.
I include 33% images at every whole ISO value for both cameras, as well as several actual pixels crops as well. The results are instructive.
Multiple comparisons are always wise, so that one can be sure of conclusions with different colors and tones and lighting. And I very much prefer real-world shooting over perfect studio lighting.
I have another series coming with very different lighting (interior reddish light).
B&H Photo has the Canon 5D Mark III with 24-105mm f/4L zoom in stock at present.