SteveR wrote:
Unless you got a lemon, your 200-500mm should be a good lens. Test it yourself and see if you're satisfied with the sharpness at various focal lengths and apertures. What about you? Are YOU happy with the sharpness of your other lenses? When you come to the point that you're dissatisfied with a lens, that's the time to move up.
I agree. Also, one lens can be technically sharper than another, but it usually comes down to speed and confidence in getting acceptably sharp pictures in different situations. How a particular lens behaves in your hands in your own cameras can matter more than lab test results.