There is some info on this page: http://www.dpreview.com/reviews/NikonD3/page20.asp Scroll down a bit to see iso/dynamic range info. All based on jpgs as far as I know, but the pattern might still be insightful. (A bit further on they state the D3 (same sensor as the D700) RAW files add to about two stops of extra dynamic range.).
ISO 100* - 7.5 EV ISO 200 - 8.6 EV ISO 1600 - 8.5 EV ISO 6400 - 8.0 EV ISO 9000* - 7.7 EV ISO 25,600* - 6.6 EV