I agree that the current generation of bodies have better high ISO performance than the D300. That said, Comparing the D300/D300s to the current generation of bodies in not a fair comparison. Compared to the previous generation (before the D300) of bodies (D2X, D2H, D200), the D300 has about a 1.5 to 2 stop advantage in high ISO performance. The D3 and D700 have about a 1.5 stop advantage on the D300/D300s, but they are FX bodies. The D7000 and D5100 have about a 1 stop advantage over the D300/D300s in high ISO performance.
I expect the D400 to perform at least as well as the D7000 if not better regardless of the number of MegaPixels. I would also expect it to have a FPS rate at least equal to the D300s. Unfortunately we will not know the actual specifications until it is introduced. I think most of not all of us feel the introduction of the D400 is well overdue. Good Luck and Enjoy your Nikons!