The 200mm f/2.8 is a very nice lens, but how much will you be using the 400mm focal length? Be forewarned, birding is very adictive! If you plan on spending a fair amount of time birding then the 100-400mm will be much better suited. If not then the 70-200mm f/2.8, 70-200mm f/2.8 IS and mark II version would be a much more versatile if you decided on waiting and saving up for a nicer lens. The 70-200mm II actually has better IQ then the prime. Off the top of my head I believe the 2x will slow down the AF speed about 2 times slower. Don