Considering Sigma 300mm f/2.8 + TCs for action shooting - Nikon (D300)

Thanks for the interesting inputs here. I am interested in the 400-600 range (DX) hence my curiosity about performance with TCs. With those 2.8 lenses i am not so worried about IQ but more concerned about the AF speed accuracy and responsiveness with TCs (especially the 1.7x & 2x). I can't afford either new and in the used market the 300 2.8 is similarly priced i think with the current edition of 120-300

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