Expect that using the 1.7 with the 200-400 will slow down AF, and remember as well that you are going to lose a stop and a half of light, which will also affect your AF. Learn the foibles of VR, if you ride the shutter button, don't forget the settle time, you can inadvertently end up out-of-focus if you are not careful, especially if you do focus and recompose. I use the AF-On button on the D200 constantly, which helps to avoid this. My wife, who uses the lens as well, does not like using AF-On, and she gets good results as well.
As to this notion of body matched to "pro" glass, personally I have used the "pro" lenses with D2H, D200 (with and without MB-D200) and D70, and the only difference is how I have to balance the rig on my tripod. Now, you WILL see differences in handling as you move "up" the body chain, mainly in how well they will drive the AF on the 200-400, but that is also the case on every lens.
Which brings up the use of the lens. I quite often handhold the lens on my 2nd body while I have the other body with a 400 f2.8 on the tripod. It is heavy, takes practice, a lot of practice, so don't be discouraged. If you are tripod mounting, be sure you have a solid one. This combo generaly sat on a Gitzo 1228 with a
Jobu Designs Jr. Compact Gimbal attached. Your freedom of movement and stablity of the lens/camera combo will be far superior with a gimbal of some type versus a ballhead.
As to "better", well, of course there are. For reach and quickness of AF, a 400mm f2.8 mated with the 1.7 is "better". For more reach, a 600mm f4 with a 1.4 is "better". Then you get to the Sigma 300-800 and the 800, and for reach they are OBVIOUSLY better :biggrin: And all of those will focus faster than the 200-400 with the 1.7 TC. If you are shooting static subjects, no big deal, but if you want flight shots, be prepared.