I doubt you'll get 1.5 stops or greater. I think you'll see a 1 stop improvement over the D200, but I mean.....honestly......even the D80 had a 1/2 stop advantage over the D200, all with the same sensor.
By the time the D80 came out, Nikon had more time to tweak the processing for the sensor, which was why the D80 takes slightly better photos.
I'm going to wait for the D80's successor. I would love the D300, and I feel that it would be the perfect camera for me (ie: arguably too much camera for me,but it would give me everything I want and never leave me longing for a better camera). Unfortunately, I can only afford the D80. I want to see the "D80s" use the D300's sensor, but include similar AF points to the D80, 5 fps shooting, and leave it at that.
If the D300 drops in price by that time, I may consider the D300 over the D80s, but I doubt this will happen.