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I am assuming your 300mm is the screw drive model. I owned the same lens at one time, and used the Kenko 1.4 tc, as the current Nikon tc's will not AF with screw focus lenses - AFS only.
It was very sharp, with nice color and contrast. On a D2xs body, Auto focusing was slightly slowed, especially in low light, but over all it was a solid package. They make two versions, that I know of, of the 1.4 tc. One is about $90.00, the other about twice that price. Sorry, I don't remember the exact models numbers, but mine was the more expensive model. Seemed very well made.
A few years ago I moved up to a 300mm afs vr f2.8. Using my Kenko tc on this lens, it also worked very well. Since I had invested a fair amount of bucks on the new lens, I decided to try a Nikon 1.4tc to maximize its performance. I found the Nikon tc focused a lot quicker, and produced slightly better sharpness as well. Also cost more then twice the price of the Kenko. For your lens, the pro model Kenko is a solid choice. It offers solid performance, and with its ability to AF with both screw drive and afs lenses, it is quite versatile.