80-400VR AF speed

I was recently reading a revew (by ken i think) on this lens and it mentioned that the AF was very slow and was quite a bit slower to the 70-300 ED how does this compare to the 70-300G?
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zeb00 wrote:sorry i dont think i made the question very clear. i was just wanting to compare the autofocus speed of these two lenses. but if you have used it to shoot f1 cars then i am guessing it is fast enough for my needs