Currently using a Sigma 150-500 on my 7D. Shoot primarily bird photo's. Looking at 2 options
Sell sigma and get 100-400l
Keep sigma and get 400 5.6L
Read numerous reviews on both Canons. A bit torn on which way to go. Like having zoom in particular when shooting smaller birds like warblers where I can get relatively close. 400 would be a great lens for shooting shorebirds and understand its excellent for bif shots