I just upgraded to the D800e from a D300s. I cannot express how impressed I am with the images and detail. I never had a complaint about the D300s, thats for sure. But the difference between the two is more than just quality of images, it is build quality, feature set and the fact is still has a DX mode for your D300 lenses.
IMHO, you can't go wrong with picking up a D800/e.