Jeff at the Dpreview forum got to play with the D300 for a few hours. He approves that the D300 is indeed 1 to 1.33 stops better in the noise department.
“I took identical shots with my D200 at ISO400 and the D300 at ISO800 and higher. I would estimate that the D300 is 1 to 1.33 stops better in the noise department. However, since the D300’s base ISO is 200, this is to be expected. Don’t expect a revolutionary change over the D200. However even one f-stop is nothing to complain about.”
He made a few further observations about auto-focus, 14-bit RAW mode and so on. Read the full text at Dpreview…