Nobody really knows optimal in-camera settings yet.....not for every different situation, anyway. I'm interested as well.
I'm picking up my D300 next week.
Opted for it over the D80 and its replacement, which probably isn't coming any time soon (soon = within 6 months). I've played with a D300 yesterday. This D300, while expensive, is going to be the last camera I purchase for a LOOOOOONG time. I doubt we'll see anything other than incremental improvements anyway.
From what "tests" I've seen, noise reduction (NR) should be turned to low. There's no need for much NR. The noise that's produced is quite OK.
Judging from samples, I'm going to have to say that the handling of noise is pretty much a tie between the 40D, A700, and D300. Anyone who says there is a noticeable/relevant difference that's actually important to their photography is just pixel peeping particular examples. Choose other examples, and the advantage goes away, and it's a tie again.
The improvement of the D300 over the D40X and D80 probably depends on personal opinion and situation. While the D300 is better than the D200, I really can't imagine it being THAT much better. I'm guessing 1 stop or less, which is what's being reported by others anyway. Of course, others are so happy about this 1 stop advantage. I'm really not that fussed about it, so excuse me for being unenthusiastic.
I'm going to keep Active D-lighting off as well for now unless I know for certain that I'm in a high contrast situation AND shooting at ISO 800 and below.
I'll be taking this be-yatch to Japan this Xmas.