I think just about all of these zooms become soft to varying degrees at 300 mm. Unless you need 300, the 80-200 f4.7-5.6 is a surprisingly sharp little lens.
I've gotten good results from, and can recommend, the Sigma 70-300 APO Macro f4-5.6. Be sure to get the APO version, as there is a less expensive one that is not as good. It too, though, is a bit soft at 300 mm., although it is good at f11-f16 at that length. Joe
