>"Even though the 16-35 f/4 is not labeled as a professional lens"
>>The 16-35mm is a gold ringed pro lens and NPS recognised
I understand what you're saying. However, my 24-120 f/4 has the "gold ring" and it would be very debatable if that ring places it into the "professional" lens category. The build quality is not as good as the vaunted trinity consisting of the 14-24, 24-70, 70-200 f/2.8 professional lenses. Also, as much as I would like it to be, I doubt the 24-120 is as sharp at f/4 as the trinity is at f/2.8.
At one time the "gold ring" was the "professional" label, but recently Nikon has diluted that distinction.