I had a few minutes to play with a Nikon 600mm f/4 VR lens recently but only had a Nikon D70 handy. Hand held, I aimed the lens across the street and these are two snapshots I got. What major zoom distance on that lens. The clarity is pristine and the depth of field is perfect!
I personally would have no use for this lens, but if I was hired to photograph a major sporting event then maybe I’d rent one.
Caution, this lens is extremely heavy. Hand holding for long periods not recommended.