I am looking to get a longer lens for middle/high school lacrosse and other field sports. From what I have read the 300 mm f4 might cover a lot of the photography I like to do sports, wildlife, and I do like portraits with the longer lenses. I was wondering if the 70-200 f4 IS would be a better choice as it seems to do very well. I cannot afford the 70-200 f2.8 II. I am also considering the 100-400 L but am worried it would be too slow. I would be pairing the lens with a 7D. Thanks for your advice.