Mike, the difference is incredible. The 200-500 is so much better. It's sharper, more accurate in autofocus, the VR is better, and I really haven't noticed the extra 1/2 pound in weight. I have noticed the difference in 500 and 600 max reach when shooting, but the Nikon is so much sharper that I have more room to crop. I still think I got a lemon when I got my Tamron 150-600, because I know many other people have gotten great results. I wrote the Tamron customer service head yesterday to see if he can do anything for me. We'll see.