Hello, so I'm looking at getting my first DSLR, and I'm looking to go with the Nikon D500. I haven't really decided on a lens yet. I think I'll go with the Tamron 150-600 G2 or Sigma 150-600 C. I've read that the Sigma has slow AF. If so is Tamron's AF quicker? I'd like to have a lens with good af to get the full potential of the D500's AF, and to be able to capture birds in flight. Which of the two would you recommend? Is there any other in that price range that would be better on the D500? Thanks in advance.