Are you taking in to account that the 300mm 2.8L is going to weigh several pounds more than the 300 f4. It gets fairly large with the hood attached and it is not what I would say is a walk around lens. I took mine with my 5D Mark II to the zoo today, I bought a shoulder pack just to carry it in because of its size. It is a work out carrying it around and using, but the pictures are awesome (thats why I put the extra effort in to taking it).


I take it you are taking a lot of pictures of birds in flight and things moving. That your comparing the 7D to the 1d Mark 4 because you want the fast shutter speed. Otherwise you would be looking at the 5D mark II since it would have the better IQ.


(just like most of the responses you have gotten) I would go with the 300mm 2.8L and the 7D if I had to choose one over the other. With this combination you have lens that will get the most out of your camera. With the other combination the 300mm F4 and 1D mark4 you would have a camera limited by its lens.