looking good Jeff :t: especially if it is any good for BIF. Also an enormous plus for anyone who is reach limited will be if it is any good with a 1.4x tc.
BIF was the biggest con for me with the Tammy 150-600 - I was on the estuary in really good light and it would not lock on to distant flying Curlews, I repeated the test several times all with the same result it seemed as if the contrast was not enough for the lens to AF. The following day I took the 400/5.6 as well and tested that with a 1.4x tc attached and it locked on to flying Curlews no problem. I switched back to the Tammy and once again it refused to lock on. The Tammy is fine for reasonably close perched birds but even then it can labor a bit with poor contrasting targets. It will be interesting to see how the Sigma 150-600 non sport measures up to the Tammy in terms of price, weight and performance.
Roy, that was my exact problem with the Tamron. When faced with close-up slow-flying birds, it gave an even more infuriating result. Each other shot was out of focus despite the shots before and after that shot being perfectly in focus. I have never gone back to the Tamron since.