I just wanted to report that this combination works really well! The D3 is the first DSLR I've used that can make this combo AF properly. I've always been hesitant to use my taped Sigma 1.4 tc with the Sigma 500mm, but it works flawlessly on the D3. Minimal hunting and it locks focus almost immediately. In fact this combination works better than the 200-400 VR with the nikon 1.4 tc, which I find hunts quite a bit. I find this combination to also work better on the D3 than on the D300. On my old D300, I could never get a sharp shot with lens+tc, perhaps due to pixel density, the D300 AF, etc. Seriously, I think this is the reason you pay the premium for pro-bodies. People don't realize it, but when you start shooting with super telephotos this is where you see the difference. Also I've been thinking of dumping my Sigma 500mm 4.5 for over two years, but it's sharper than my 200-400 VR, weighs less, and I paid under 3k for a pro caliber telephoto. No wonder you can't find these used! No one gives them up!