The question was asked sometime ago - is the O.P. still looking for a long lens?
I had a XXX-600mm (or xxx - 500mm) on my LLL (lens lust list) for a long time before pulling the trigger with this year's income tax refund.
I had the chance to try both the Tammy and Siggy xxx-600mm on my D610 in the store. The clerk asked if I had considered the 200-500 5.6e. I had not. He put it onto my D610 and I tried it. Although it is not as wide (200 vs 150mm) and not as long (500 vs 600mm) I was impressed with that first feel of the lens and the speed of the autofocus of pedestrians across the street through the stores front window. Beat both Tammy and Sigma. If felt better. i also have a D5100 and he said it would focus better on that one too. Although I've not compared them.
I did a little google research and read on-line reviews over lunch while we talked about it. The Nikkor is the most expensive of the three, but when dropping that kind of change, what is another hundred or two (or three)? Siggy plus USB was not that much cheaper. Tammy was the cheapest. As you can see from my signature, I'm a Tammy fan and love their lenses. But this Nikkor is the best of that bunch, IMHO.
I have not regrets and love my 200-500, no regrets whatsoever.