Huntnphool covered all the info, (and after seeing the pics he and others on here post, I take his word as the gospel truth). I would like to add one thing though. I had both the IS L series 70-200's and ended up selling the f-4 and kept my 2.8 to compensate for the loss of stops when using a 1.4 or 2.0 teleconverter behind it. The 2.8 is a bit heavier, but I've always been able to hold a heavy rifle steadier than lightweight one, so I don't mind.
Hopefully someday I'll find that legendary money tree and be able to afford a great big white prime lens, but until then, I'm stuck with crop-frame sensors and teleconverters.