Lemme get this straight...you have the 70-200 f/2.8 L IS? I'd ditch the 1D (+$500), get the 2X II extender (-$300) for the 70-200 2.8 (making the need for the 100-400 redundant) and get the 1D Mk II used (-$1100) for net expenditure of $900. You get what is possibly the best camera for the money IMHO- the 1D Mk II *and* you have up to 400mm L IS at f/5.6. Best of both worlds in my book....