The new Sigma 24-70mm f/2.8 DG OS HSM Art lens for Nikon F-mount is now shipping worldwide and is currently in stock at:
B&H | Adorama | eBay (refurbished) | Amazon US | Amazon UK | Amazon DE
A good and very detailed comparison between the Sigma 24-70mm f/2.8 Art and Tamron 24-70mm f/2.8 G2 lenses can be found on krolop-gerst.com and on makofoto.cz:
Lensrentals published their sharpness test for the Sigma 24-70mm f/2.8 DG OS HSM Art lens (see also this post).
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