Whether you will really carry around a lens the size of the 70-200 2.8 is a real consideration.

It was the deciding factor for me and I was looking for the 70-200 f4 IS when I came across a 200 2.8L at a price I couldn't resist as it was not heavy, its very sharp and is relatively small. I may ultimately go for the 70-200 f4 IS for the versatility - so size was the determining factor - no point having it if you always leave it at home.

Good luck
Josh