Manuh,
I know that you said a headon shot at 300mm. This one is a quartering away shot of the same deer at 300mm, f5.6. I shoot using AF-S mode because, as stated elsewhere, the AF-C mode is not really good a predictive autofocus. That means I have to bacsically recompose each shot I take of a running dear, literally while panning the action. Do I miss some, yes. Does the camera and lens combination lock on when needed, more times than not. Is this shot perfect, no, but it is my shot, taken with my camera and I would feel the same way if it were a sony, canon, nikon, panasonic......
I use my tools within the limits of their design and accept the fact that in real world terms, that apply to everyone, every design is a compromise, everyone survives by compromise whether they believe it or not. I am a professional aircraft inspector. Every aircraft that actually flies is designed, manufactured, and operated on a compromise. So are our cameras.
To answer the poster above who wondered how many people posting to this thread actually have used a cameral with a world class autofocus system. I have. I cannot afford them. So, I use what I have and use them within their limits. I chose to post samples of the system working. I am sure everone here could post the same.
Many of us could post just as many of the system showing it does not work.
That would get us no where. Basically a stalemate. And that is where this thread has gone. It is Sunday, maybe we should take a rest and get back to taking pictures for the love of photography. I hear more deer calling my name.