Hi Colin, I have used the 600/6.3 pf twice so far. I can say that sharpness and usability are its characteristics. Considering the alternative (for me the 600/4 TC) it is worth every penny. I got the lens from a friend who has a lot of money and buys most primes Nikon produces. He, usually, keeps the most expensive ones. It cost me 3950 eu. I consider myself lucky. If you need the mm buy the lens, you will not regret it. AF is fast.