i'm owning the canon 90-300 USM which is more or less the same as the 75-300 usm besides the range that it covers, and i'm also owning the sigma 70-300 APO. in terms of output quality, sigma win hands down.. but in terms of operation, my 90-300 USM focus much faster under lowlight condition, and the sigma will hunt around having hard time to focus.. but then, under low light condition, these tele lens wouldn't be useful unless ur subject is static, and u have a good tripod with u.. hand held shooting @ 300mm under lowlight is going to be blurry.. planning to let the 90-300mm USM go for cheap.. PM me if anyone is interested..

This post has been edited by kevin613: Aug 24 2007, 11:35 PM