The 70-200 f4 is a great lens, if you can get by with what you shoot. 1 stop loss of light... well still not so bad again... based on what you are shooting. If indoors in somewhat a fair amount of ambient you may just be able to get away with it. Once again though, I would try and demo/rent the lens first for verification. If you don't mind shooting aftermarket glass, then the Tamron may just fit the bill, their VC on the 70-200 F2.8 is also a great feature. So guess it really ends up being about how much you are willing to sacrifice. Weight vs portability, as the F4 is easier to carry around on the shoulders, and less of a burden if you are shooting in a crowd vs the F2.8 (in any mfgr).