100-400 is a 1500 dollar lens, its only f/4 though. I am looking at a Canon 70-200 f/2.8L right now.
hey, i didn't know you where also interested in photography?
in the Anet forums, there's an interesting discussion going on about the 100-400 or the 70-200 with convertors instead.
the 70-200 as you said has a wider aperture, but the focal length...not enough for airshows :( it's light though (half the weight of a 100-400) and has a third generation IS, the 100-400 only a second generation.
both are extremely high quality lenses...but also expensive. i hope i can afford one of these two next year ;)