I wasn’t pleased with the Sigma 50-500 when mounted on the Canon 5D Mark III. The 1DX makes the high ISO acceptable, and puts this lens in a category of its own.
The 50-500 range makes this versatile beyond all other lens. Coupled with a Sennheiser MKE 400, Manfrotto fluid video mono pod, and the Jobu jr. gimbal, this is a unique video, photo duo with no peer that I know.
ISO 4000, f/6.3, 1/400