Image quality results have been added to the Sigma 24-70mm f/2.8 DG OS HSM Art Lens page.
Let's get right into some comparisons:
Sigma vs. Canon f/2.8L II
Sigma vs. Canon f/4L IS
Sigma vs. Canon 24-105mm f/4L IS II
Sigma vs. Sony
Sigma vs. Tamron
Sigma vs. Tokina
Many other comparisons are available and we'll have some additional 24-70mm comparisons available when the 1Ds III image quality results are posted (soon).
The Sigma 24-70mm f/2.8 DG OS HSM Art Lens is available for preorder at B&H | Amazon | Adorama | WEX.