The D700 is a great camera, but with just a $200-$300 price difference I would go for the D3, because
1) The controls are different — switching will never be quite automatic 2) The shutter is not quite as responsive on the D700 — this really used to annoy me with work's D700. I used to bring my D3 in rather than use it 3) The lower weight makes for less image stability — unless you get the battery grip, in which case the price differential has gone
When the D3 was top camera, the price difference was more like 2x. There was a reason for that.
You might want to consider getting a D800. It has the same ISO range as the D3, more advanced electronics, and that amazing 36MP.