and to throw spanner in the works what about the sigma 150-500?
though looking at all the reviews, images, youtube vids and whatever else ive found over past few weeks the tamron does seem to be the better lens. the OS on the tamron supposed to be excellent, and of course its got 4-5 years advancement in lens technology over the sigma. some have even said its better than the new sigma 150-600 where a few people have had some major issues . i guess though with any lens in this kind of zoom range there will always be a few compromises but for the money i dont think you can honestly lose out whatever one you choose. if you wanted ulta pin sharp then the choice is a canon L prime or similar but then your paying serious amounts of money for that.