I think the combo works pretty well. I am enjoying using the D3X this summer. As you know, we don't have a lot going in the way of bird photography here this time of year, well, actually the shooting is just as good as ever, it's just not a lot of fun being out in the heat, humidity, and bugs that we have this time of year. So I have been shooting storms.
I'm waiting for the Eagles to start up again in October. The D3X works great with the 200-400 VR lens too. I'll post another shot of a bird taken with that combination so you can see that.