While your friend is offering you a D3 for only $150 more than his D700 (what a great guy!) there is a reason the retail price of a new D3 was almost $2000 over that of the D700. The D3 is not just a D700 with a built-in grip. While the image quality of both is the same - the D3 takes build quality to a whole new level and just works quicker and faster. For $150 more its a no brainer IMO.