Tokina at-x pro 300mm f2.8 on D800

Hi all

I am considering buying a used Tokina AT-X 300mm f2.8. Can't find that much info about this lens when used on a high res dslr.

Does anyone here have experinece with it?. I can get a mint version of this for $1400.

Note: I already have nikon 70-200mm I f2.8 and the tc-17 II. Should i save more mony and look for å 500mm f4.5 insted ?

(Will be used for birds etc)

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Thanks