I owned the Tam 100-600 for two years and well it was always a struggle . The picture was never quite sharp ..was it the back focus? Was it as bad copy ( its in Portugal now ) you always wanted to fiddle with it but in the end it was just soft . Most of the birds in the Somme re at least 60 yards away. Out of 500 pics of birds you might get 10 that you were 50% happy with. The G2 version is supposed to be better at the edges but softer in the centre so NO NO that's even worse. All comparisons done with a D7100 at F8. So now we have the 200-500 . well what a change . All the shots where it was not operator error were brilliant . You could now wait for the bird to smile at you and get a good pic. Focus always spot on even if it was on the twig in front of the bird ..but that's my fault. The 100-400 tam was equally good allowing for the fact that you had to crop a little more it was a great light lens ideal for the wife to carry for a couple of hours. Photos of the same bird from the same spot with each were almost equal when cropped to match. Forget the console just do the FFA the old way at 400mm on a target at at least 60 yards. A 1.4 teleconverter would not work with the Tam 100-400 , display went crazy . It worked on the 200-500 but reduced the quality to Tam 150-600 levels. I paid £802 ( Rec £1150) for the Nikon delivered ( $1100 ?) and £465 for the Tam 100-400 maybe $600 . so Nikon you can forget your 600mm F5.6 P thing at what maybe $5000 ,I will stick with the 200-500 thanks .