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My backpack must weigh over 15 kg full of camera equipment and supplies. I don't know if I'd notice an extra 500g. On the other hand, I don't know if I'd notice an extra half a stop at that focal length.
All these lenses can be expected to produce good results, but the pre-OS Sigma 150/2.8 is outstanding in the company it keeps. There may be differences in image quality among the current set of lenses too.
The IS in the latest 100mm macro is supposed to cancel lateral vibrations, improving quality near close focus. Do any of the long lenses have similar reduction? I don't know what's inside Sigma's "OS".