Why not consider the sigma 70-300 f4-4.5 Macro? Reviews for the lens has been quite good. Think quite a number of them for sale, 2nd hand in the B&S. Only short coming of the lens is that the focusing could be slow and no IS.
One of the problems when u use the 300 mm is that you'll prob need >1/500 shutter speed ( based on the 1/focal length rule. So without IS, the 70-300s are usable only during day if you hand hold. Think it's not very usable indoors because of the speed.