The Race to High ISO
As good as the 5D Mark II is, this examination of high ISO noise shows me one thing: above 3200 ISO, IQ is generally crap, regardless of what body from what manufacturer. Looking at the pictures, the 5D Mark II at 6400 ISO is decent but I wouldn’t be happy with it.
Consider the D700:
Again, at 6400 ISO, it’s decent but I wouldn’t be happy with it.
So in general, this race to high ISO is much like the race to high megapixels: it’s bogus crap.