For the sake of keeping my lens collection in Nikkor, I decided to purchase Nikkor 80-200mm F2.8 over Sigma 50-500mm F4-6.3. Cross-fingers for any regrets but a little bit relieved though. The rating for the Nikkor lens is 9.4 (not bad).

Here are some of the shots I had using the lens. Images in BG were taken using my Nikkor 18-135 though.