Richard, I would keep the D700 and D7000 until the D800 and D400 are in your hands. Neither will go down much in value over the next 6 months but fluctuate with supply and demand. A perceived flood on the market, will drive the price down and then it should recover.
I am beginning to think that it would be better for me to use the D800 with a smaller JPEG size than DX crop mode for Events. 4fps is what I now shoot at, I would not use 6fps. Evidently the tracking would be the same and I would have more viewfinder to look thru.
I don't like the idea of having outside the crop area shaded. Do you think that shaded area will be blacked out or will an object be visible thru it?