You do not list OS in your 150-500mm Sigma lens specs. Your review then is in the wrong section of the legacy lenses, citing the wrong lens. Please remove your review and put it with the earlier release, which did not have OS and has similar results to yours on the longer focal lengths.

Hand held the Sigma 150-500mm APO, OS, HSM will not produce the same sharpness as mounted on a monopod or tripod with a ball head or adjustable head set with slight drag, and with the in lens OS on. You have lowered the overall user tests sharpness results, apparently by hand holding at the longest focal lengths, and giving no alternative support references. Any 400 or 500mm lens hand held will require for sharpness what you do not offer in your review: adequate support, and adequate shutter speed (Usually with the latter comatching the focal length to get sharp results). If one could get very sharp results with the longer focal lengths by hand holding such a lens, everyone would be doing so -- NOT!.