I was thinking about saving up for a 70-200mm F2.8 and the Canon is $1700 with IS, $1200 without, Sigma has one for $799, and the Tamron 70-200mm F 2.8 is $699. Does anyone here have the Tamron, what do you think of it? My question is, Do you think that the Tamron will have comparable image quality and focus speed to the Sigma and Canon? Is it worth it to spend the extra $$ on the Canon or is the Sigma, in the sweet spot for bang for the buck? Or should I sacrifice the 2.8 for more zoom and just get the Canon 75-300mm (non IS) for $200? Thanks.