Yes it will be different at high iso than a D3
Yes it will be different at high iso than a D3
It seems likely that it will perform similarly to a 1Ds3 at high iso, or maybe as well as a 5D2 (which canon suggest is a bit better than the 1Ds3). That is the per pixel noise will be higher than the D3, but the pics will be fine. Even Nikon can't buck physics.
As for the article suggesting that there is no visible difference between a 12Mp camera and a 21Mp camera when assessed via a 13 by 19 print - if all else is fairly equal it's just not true. If the image needs resolution you can see the difference, which is not to say that the 12Mp output is anything but good or that clients can tell🙂
Mike