it'll give you 1 to 2 stops improvements - i.e. ISO 400 on the D300 should be as good or slightly better than ISO 200 on the D200... if you normally shoot at ISO 400 or below you probably won't notice much of a difference.
I did buy a D300 and now use my D200 as a backup - I rarely need the low light capabilities, I upgraded primarily because of the autofocus anf 8fps ability...
I have two D200s and a D300. The D300 has about 1 stop better noise performance when shooting in RAW (i.e., real noise performance, not JPG noise reduction). It also has modestly better resolution due to the higher pixel count, and somewhat better focus options. Otherwise, the two cameras are very similar.
Very few people can use all that a D200 has to offer, much less a D300.
Hi, I dont really know how it D200 compare to D300. I am upgrading from D50. For me it is so much difference in term of fast focusing, exposure under mid noon sun. , more shot per frame. You should consider beside ISO performance. Another big plus is fast focusing and predictive dyanmic tracking which make sport photography more easy to take. Someone just shot a Owl flying at sunset with predictive focusing . See futher the forum there. So it depend what kind of subject you like to shoot . Don't upgrade just because it is better because I believe that later Nikon will come out something better. I have friend who have D200 and they are putting on hold as they normally shot portraits.
Upgrade according to your usage in that field. For bird wild life and sport photography, then it make sense to upgrade if you are in this subject you like to shoot.
Two stops improvement in low light performance v. noise. My ISO 1600 shots with the D300 look as good as the D200 shooting at ISO 400. And that was pretty dang good to begin with, about like old Kodachrome 64!
Dynamic range of the sensor is also much improved with the D300. I used to regularly blow highlights or block up shadows with the D200-- very infrequent now with the D300.
AF is much better, with noticeably better low-light performance.
The LCD is vastly improved (the info button readout on the back LCD will be especially appreciated by anyone handholding a long lens).
Battery life is easily twice what the D200 offered with the standard EN-EL3e, with a greatly improved design of the vertical grip and better battery life and speeds with AAs. Frame advance rate is on par with other pro offerings using the grip, and a none-too-shabby 6 FPS without.
The D300 may look like the D200, but at heart it's a pro camera, not just a prosumer one. It is positioned to replace the D2X, something that the D200 did not quite aspire to do, on several levels.