1/1000 shutter speed should give much sharper results at 510mm. I can't imagine anything sharper than 70-200VR f2.8. TC17E II has 1.5 stop light loss so effective f8 has master lens at f4.8-ish.
Have you considered TC14E II - a great TC I use with 200-400VR to give 560mm f5.6.
What camera are you using?
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