Do you believe that I sold my Nikon 200 -400mm f4 lens after trying the Tamron 150 -600mm? Yes, It's true.
If you read the reviews of the Nikon 200-400 f4, many photographers confirm that this lens is not good at infinity, the same goes with the Tamron as well, so why pay more for this Nikon lens and carry this heavy lens all around?
The Tamron is very sharp at close range, sample attached,
Conclusion: If you want a cheap lens that produces good quality image, then go for Tamron 150- 600MM, you won't be dissapointed!