Never mind the shooting, IS is great when composing images. I won't buy telelenses without it anymore, and I would not get the 400 for that reason.
But may I ask why, if you haven't more than 85mm of reach, you're not considering one of the 70-200's? Insanely sharp, brilliant IS, about your price range if you choose the f/4IS. With a 1.4TC you have a 280/5.6 IS lens that is only lacking a bit in corner sharpness if you ask me. OK, maybe a little more than a bit if you take a mark II TC... AF speed is significantly lower though.
wildlife (less time) and events outdoors (more time).
I was think EF 200mm f/2.8L II USM for the events and a 300mm or 400mm for wildlife (mostly zoo for now). Any of these three focal lengths i will use. I'm just not sure.