I have a Nikon D610. I am looking for a general use wildlife lens/lens combo. Price is not an problem in comparing these two lens/combinations. I any case I can't go over $2000 dollars. I know the Nikon combination does not have VR and the Tamron does but is this enough difference to get the Tamron? Image quality is a concern as well as the speed of the lens/combo. Any help would be greatly appreciated.