Unless you need the f/2.8 for DOF or low-light shooting, you could go for a used Canon f/4L version. Lot lighter, smaller, and just as sharp (if not sharper than the f/2.8 version) and same super-tough L build quality. I see them on CL for $500 or cheaper.

I don't have any experience with anything in-hand than the 70-200mm f/2.8 IS and the non-IS f/4L, so I can't be of any help picking between the other brands.

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See my user profile for gear information. Then forget about that stuff and go take pictures! And then some more pictures!