I think the D800 is going to beat the D700 in every way but frame speed and I shoot at 4fps now so that will not effect me. Improvements in focus speed, white balance accuracy, face detection, and active-D lighting will make up for having to use a higher shutter speed. It will be great for capturing fine detail when there are a large number of people in the picture. And more potential customers are asking me if I do Video at weddings.
But the ultimate camera will be the "low light" D4.