I spent a lot of time in the Nikon booth at Mac World last week working on just this question, D200 or D2X. I used both, and looked at the issue from a totaly underwater prospective.
Interesting, as the Nikon sales people kept trying to convince me that the D200 was he way to go...
When I took low light higly saturated test shots, and then did test prints, the X still looked more saturated to me.
OK, as an S2 shooter, I am all about the look and saturation. I am often accused of over proccessing with the S2, but I know better. It just looks beter than most. I know, we can have all sorts of "arguments" about it, but the D2X is the first sensor I have seen that matches or exceedes the quality I see in the Fuji.
The D200 does not seem to have the same saturated look the D2X has. OK, the autofocus is fast, and they "claim" Cam-1000 is as good as Cam-2000, but I am not convinced. In really low light situations, using a 105mm, I "felt" that the X was really faster.
Trust me, I wanted to find an excuse to lower my expectations for the 200, so I could save 3 grand on the next purchase, but I left the show wanting the D2X.
Hope this helps a bit...