I seem to be in the minority of people who still get excited by increasing maximum ISO speeds. But can someone explain, why/how is it possible that the difference between maximum base ISO (25600) and extended is 4 stops, whereas in Canon cameras (the 1DX/5D3 at least) it is just 2? Does it make a practical difference? Is it just another means of notating it? In my experience (300D->50D->5D3) the highest usable ISO is 1 stop below maximum base ISO (depending on what you're using it for). So extra extended settings would be irrelevant. Is Nikon different?
They could extend it 100 stops if they want. Big question is... how useable / how noisy is it?
Just because the camera says it can do 409600 ISO does not mean you would be happy with it. Until we see what it looks like at these high ISO, only then can we judge what is useable.
From what I have seen out of the 1Dx, some of the high ISO images are actually quite good.
Would be interesting to see if the Nikon can capture anything close to this at 25600