I understand that while a professional may need to spend seroius money on camera equipment, it is often the serious amateur, unconstrained by issues such as cost / benefit that will go for the "best of the best" without a lot of debate as to what that equipment will add to a given shot.
I would agree with the above conclusions that:
1.) the D200 appears to offer (slightly) better dynamic range then the D2x
2.) the D2x offers better low light focus (IMHo with faster speed / lockon and much less "hunting")
Full frame, offers some serius tradeoffs. My canon 5D offers magnificant image quality, large DR, very low noise (even at very high ISO), all in a package that is quite lens finicky, slow, poor AF in low light (unless with fast lens), and clunky to handle. The D1sMkII (have used but don't own) fixes the "clunky" factor (except for the ridiculous weight due to older battery technology), ups the focus effectivenesss in low light. I believe the 5D files currently excell over the Mark II files in image quality in general (just my take on it).
I am hoping that nikon full frame will be more mature, even at introduction, offering retro-compatibility with DX lens's (in a high speed crop mode), but it remains to be seen if Nikon lens's will be less affected by the vignetting issue which limits Canon's full frame usefulness.
My own take on full frame, is that I need the DX ie crop version of a medium format camera, i.e a digital back with a 1.3x multiplier (i.e. crop) in a 6x4.5cm format. There I get the nice large sensor, and still get to stick to the "sweet spot" of the medium format lens's.
Then again - that thought just illustrates how amateurs (myself) may go more for the "best box" and spend too little time considering how truely it will benefit the picture that we produce...
