thanks Peter and Erik for your comments/ feedback.
Frank, based on what you have said your intentions are, then, Mongo would say that he 200-500mm with or without a crop sensor body will be ideal for you.
BTW, Mongo no longer has a dedicated DX body but often uses his FX bodies with this lens in semi crop mode of 20 X 30 (which is about a 20% crop). This also gives good results.
