With the exception of a smaller viewfinder view when using DX lenses in auto DX crop mode, the D800 is better then the D200 in every way I can think of.
1. The DX crop photo in the D800 will give you the exact view as if you were using the D200 and the same lens from the same position.
2. Dynamic range will be much improved in low ISO images.
3. Noise will be much improved in high ISO images.
4. Autofocus will be better and probably faster.
5. You will be able to get tighter cropping because of the 15mp sensor size in DX crop mode versus the 10mp of the D200.
6. Resolution will be higher on larger prints.
You will pretty much get D7000 performance in a more robust and larger body. It's pretty hard to know what a D400 will be or even if there will be one. Since you are so committed to DX I would probably wait a little while longer and see what Nikon comes up with in the next few months.