Just posted: Sigma 150-600mm f/5-6.3 DG OS HSM Contemporary Lens Review.
This lens is a strong contender to the extremely popular Tamron 150-600mm f/5-6.3 Di VC USD Lens.
B&H has the Sigma 150-600mm f/5-6.3 DG OS HSM Contemporary Lens (Canon mount) in stock. The Nikon and Sigma mount versions are available for preorder.