I love the 300 2.8 too, but I will tell you that @ 300mm, the DoF at f/2.8 is too little for many (most??) bird shots. I find f/4 to be too shallow, and use f/5.0-f/9 using my 300 f/4. The pros buy the 300 2.8 over the 300 f/4 because it's sharper and weather sealed and (as far as I know) don't use f/2.8 as much! For sports, it's a different story, buy the f/2.8.