Upload & Sell: Off
I went from a 1Ds to an F5 to a D700. ALL were upgrades imo, but for different reasons, obviously.
D700 wasn't a "night and day" difference in IQ, HOWEVER in most every other aspect, the D700 was. The battery life, LCD, low light performance, functions (live view, sensor cleaning, easier operation, etc) were upgrades. Build quality is close to the 1Ds.
I am listing the D700 because the D300 is similar in build and feel. The D7000 feels quality as well. Have you checked out the D7000 in person? Really a great camera.