If you need this now, get the D700 and use it for several month. By then, the reviews and critical tests will be up and you can get a better decision if you want or need a D800.
If you decide you need to change, you can always offset the cost of a D3s or D800 by selling the D700. Or you might find that its all you really need.
While I love the D800 specs and if I had waited a few more months I probably would've waited and picked up a D800 when released, I have no regrets in buying my D700, new, last November. It's a heck of camera, old technology or not, it still produces some amazing images.
In the mean time, I'm saving my pennies for a speedlight, then faster glass.