BTW -- The best image comparisons I've found so far are at
Imaging Resource. They've got controlled, high-iso studio shots of the Mark III bodies and the D3 for comparison. By my eyes, the D3 has about a one stop high-iso advantage at this point???
The D3 has read noise at the pixel level almost as low as the mk3 cameras at high ISO (and lower than any other Canons), and has significantly less shot noise than the mk3 cameras because it collects a lot more photons. Because of this dual-source nature of noise, you can't simply say that one camera is noisier than another, because one may be noisier in the deepest shadows, while the other is noisier in the midtones. In the case of the D3 vs 1DSmk3 and 1Dmk3, you should expect the D3 to have less noise at the image level in the brighter shadows, midtones, and highlights, while 1DSmk3 should have much better deep shadows, and the 1Dmk3 marginally better deep shadows, especially for stuff like astrophotography, because Canon does not clip its RAW data at or near black; they leave enough of a positive bias in the RAW data that all of the noise, both positive and negative, is equally balanced and preserved near black, and is better for binning and stacking RAW images.
If the question, however, is what gives a more noise-free high ISO image when there aren't deep shadows of interest, then the D3 will give the lowest-noise images.