Oops! Yes, the lenses that I was speaking of were in fact the IS models, but the pricing that I quoted was for a used non-IS model. Sorry for the confusion.


True the 70-400 f/4 is sharper than the f2.8 I wide open, but at the cost of one stop. If you're planning to do a lot of indoor sports (poor indoor lighting - poor with respect to exposure) you'll appreciate the f2.8 (in fact you may even want faster). The f/2.8 stopped down to f/4 is nearly as sharp as the 70-200 f/4 - as either is a great lens for outdoor sports.


As far IS vs. non-IS models, some will say that when shooting at shutter speeds above 1/500s, IS is not very useful, and while that is correct with respect capturing a image; IS is still very useful for image composition when looking through the viewfinder (most especially with long telephotos - arguably not too much a worry with most focal lengths on a 70-200).