In a post at the Nikonians there is a comparision between all major Nikon cams: D100, D70, D50, D200, D80, D40x, D2X, D300 and D3, measured based on RAW files  Nikonians submitted. A good and easy way to compare dynamic range, e.g. from the D200 at ISO 200 the D300 is about 1.5 stops better and the D3 about 2 stops better.