There is no doubt Nikon 600mm f4 VR is legendary when it comes to focusing speed. Nikon introduced the new 300mm 2.8 VR ii. The focusing speed of this
new 300 is probably faster than the earlier VR version. I tested the 600mm f4 VR against the 300mm 2.8 VR ii. First, I tested both lenses at full range focus. Then, limited focus.
Then I added the Nikon 1.7 Teleconverter. And tried both lenses both with focus limit switch on and off.
Here is the result: