Any opinions about the Sigma 135-400mm f/4.5-5.6 DG RF APO? I've already got a 70-300VR but I'm looking for more reach without breaking the bank. Does the Sigma take a TC 1.4 or 1.7? What other recommendations would you make for a wildlife lens? I'd love to have a Nikkor 300mm f/4 or Nikkor 80-400 f/4.5-5.6 but even used those are a stretch at the moment. Would I be better off waiting for one of them over the Sigma?