I think it is fair to say the D800 will not have the high ISO noise control performance of the D3/D4.
It may be equivalent to the D700 in this regard, even with the greater pixel density, or it may have perform similar to the D7000, which has roughly equivalent ISO range and pixel density. I would prefer to see some real world use to see which that will be.
My own experience with using the D700 and the D7000 is that the D700 is a better high ISO performer than the D7000.
So, for those who were looking for the D800 to improve high ISO performance over the D700, this may be a disappointment.
To me, the D800 wasn't designed to address that issue, but it a completely new camera with completely different capabilities.