The best camera in Nikon mount today for high ISO/good DR/great colors is probably the Fuji S5Pro.
I appears that the S5Pro is still behind the Canon 5D in terms of detail at ISO1600, but it is ahead both in DR and color saturation. I don't know how it compares to the Canon 1DII/1DIII.
If you are looking into purchasing a Nikon body, then it appears that the 400US$ D40 (price in Japan) is probably the best in absolute detail at ISO1600.
Regards,
Bernard