Yeah made up my mind. Should be picking up my Sigma tomorrow or tuesday at the latest. Very curious how it'll perform. I love the 70-300L and will always defend it on a crop, but my 70-200/F2.8 is just plain better for my uses, I hardly ever need more than 200mm (except on vacation, but that's not that often). And I do take a lot of indoor shots, especially of my kids. Should provide some nice wedding opportunies too.
What really pushed me over, was the fact that I had the NEX6 + Zeiss 24mm (35mm in effect), and I really love that focal length, especially on our trip to South-Africe where I paired the NEX6 to the 7D+70-300L. So I guess the Sigma should be at least as good on a fullframe. Sold the Zeiss to fund the 5DIII though.
What pushed me over the edge to get the Sigma, even though I already had the excellent Zeiss 35mm f/1.4, is a detailed image-comparison review by Zeiss expert reviewer Lloyd Chambers. Chambers concluded that the Sigma was at least as good as the Zeiss, and significantly sharper and more contrasty @ f/1.4. His image comparison pushed me right over the edge.
I wish I could share the link to his compelling review, but it's part of his subscription-based review site.
You're going to love the Sigma 35 on your 5D III!