Yeah, these Canon ISO is not suitable higher than 6400. And if we look to Nikon D3S which is response to Canon 1D mark IV, we would see, that 25600 ISO is quite good for usage. But neither 51200 ISO nor 102400 ISO is not usable.


http://www.dpreview.com/reviews/nikond3s/page17.asp


But in my opinion, 6400 ISO is very good! And if you have fast glass (F/2.8 or less), you can control light whatever you want