So I guess my final choice is f4 for me, f2.8 ii for him.
I think that's the perfect compromise. It would be nice to have the 70-200 f/4 when I'm out shooting during the day and don't need the 2.8. The 2.8 IS II is a pain when I have to carry it for 12 hours.
That said, I've actually started using the spider holster system on my think tank belt. Have you considered a belt carrying system. It beats having anything around your neck or on your shoulder(s). I'd give it a try. I have a Black Rapid strap and even that bugs after a while. I hardly even feel the camera weight (5dmk3, 600ex-rt, and 70-200 2.8 IS II) on my hips/waist.