Yes, of course you're right, and I was exaggerating in "2.", above.

But actually, precisely because these cameras target somewhat knowledgeable market, I seems unlikely to me that Canon is producing a sensor which is just identical in performances to Nikon's, but at lower resolution and with a mere software tweak used to throw at buyers a "fake" ISO 25600 (and dpreview.com does not put it that way, in fact, for what it is worth). While we know that pictures at 25600 are in many cases useless, I would also reasonably expect that the whole ISO range from 6400 to 25600 does bring benefits, just as higher resolution does. One may argue which is a more relevant benefit, but still.
And, this seems to me a realistic possibility since the ISO setting is actually modifying how the sensor responds (by changing the voltage fed to it) before the ADC kicks in, so before entering the digital domain.


That actually is one of the most advertised features of the 5D Mark III. Or, at least, it is in the form of "best camera ever to take pictures in the dark", or something along those lines. Still a bold statement, I'd say, that I would expect carries at least some truth in it.