How does the 100-400 + 1.4 combo handle BIF and moving targets (aircraft)? Although I’ve been very happy with the Sigma 150-600, I’ve kicked around the idea of consolidating the (now seldom used) 70-300L and sigma down and replace with the 100-400.
The addition of the TC to the lens slows down the AF noticeably (but I shoot a lot in low light).You are also restricted to centre point for focusing plus the 4 surrounding helper points. Initial acquisition can be tough. The combo may or may not work for you depending on how and what you shoot. It isn't my first choice for BIF with fast, small, erratic birds but for bigger or slower moving subjects it makes a great, portable combo. I owned the Siggy 150-600 for a while. The 100-400 delivered better IQ to my eye even with the TC.