It's a chuck up, 300 f/2.8 IS L v2 OR 400f/2.8 IS L V2, the number of Photos I take with each tells me it's the 300, but IQ is hard to tell the difference, both these lenses (I agree with bdunbar79) the level of "awesomeness" in these two Lenses, is just, awesome ??.
quote author=bdunbar79 link=topic=13840.msg251044#msg251044 date=1364701850]
400 f/2.8L I IS. Why? Because it is just pure awesomeness. I love longer focal lengths and this lens AF's rapidly, and is razor sharp, corner to corner, wide open.