Arash:
My comments on the 200-400 came from the use of a rental lens two years ago. I shot 4-5K images with it, in Florida, mainly large,tame Florida birds. I had both the 1.4 and 1.7 TCs. In my hands, I found the distance shots to be a bit soft with the 1.7, ok with the 1.4. At closer distances, I really appreciated the zoom capabilities.
For all around birding, I would prefer the 500mm f/4 over the 200-400. If the light is low, I will use the D700 and TCs, but as light comes up and I need the reach, will switch to the D300.
Perhaps I got a bad copy of the lens (200-400)
Thom Hogan has some interesting thoughts about this lens in a review he just posted.
http://www.bythom.com/Nikkor-200-400mm-lensreview.htm
I am glad it works for you. Maybe operator error on my end.:D
Randy