I don't own a D7000, but I don't anticipate needing much more than the noise free ISO 1250 a D7000 is capable of. I have an fps issue with the D7000 and with the D800. I could easily end up buying the next iteration of the D7000 if no D400 appears. My biggest concern with the D800 apart from speed is the viewfinder.

My primary goal in a new camera is to shoot more without teleconverters. With my 500 f4 I get a reach of 850mm equivalent at a 12MP crop with the D800. With a 24 MP D400 that would be 1000mm. Now, that 1000mm intersects nicely with my normal rig: 500 f4 AF-S and TC-14E on the D300 - but without the TC. If, on the other hand, the D400 is only 16MP I'll be no worse off than with the D800 (866mm equiv. @12MP). And for the target crop in the viewfinder we're talking .93/1.4=.66 with a D400 24MP (or .93/1.15=.81 with 16MP, roughly equivalent to the D7000) vs. .70/1.7=.41 magnification with a D800. I think the D800 viewfinder image is unacceptably small.

Jim