I've owned both the Tamron and the Canon 24-70L. The Tamron I had, other then a little softness at 1 corner at f2.8, was every bit as sharp as the Canon. AF is fast as well. The shot below was done with the Tamron 28-75 f2.8 on a 5D. The first is the full image, the 2nd is a 100% crop. Looks pretty good to me!