It is sharper than my 24-105 which is sharper than every Canon 24-70 f2.8 series one I have tried.
Then you won the Tamron lottery, because every review I read says it's at most on par with the 24-105 @f4 and has problems on the long end.
I got hold of a Tamron 24-70 in a store today and compared it with some test shots to their 24-105L and the 35L. First off, the rumors seem to be true - there is a larger production variance with Tamron, because it had a healthy frontfocus that is uncorrectable on my 60d. But I could compare the lenses at the zone where the af ended up. If I ever should get the Tamron, its probably best to buy five lenses, test them and return four.
The iq of this Tamron copy was a big letdown, at f2.8 its very underwhelming (even on crop!), and nearing the 24-105 at f4. The 35L in comparison is a class of its own and knocks your socks right off, it's as sharp at f1.8 as the Tamron at f4. VC seems to be ok, but really, at ok indoor lighting and open aperture its "nice to have" but hardly essential - the shake at these focal lengths is very low anyway, except if you're shooting video or handheld hdr. The Tamron af is noticeably slower than the 24-105, but faster than the 35L - someone please try servo af and lots of consecutive shots and tell if the Tamron is precise.
Since the 24-70vc & 24-105L cost about the same, the f2.8 of this particular copy is for small print only or emergency use, esp. in combination with the vc. And you trade it for longer zoom range and better af. I hope lots of 5d3 owners sell their "crappy" kit 24-105L lenses and they end up with people who can appreciate them. But I'll try another 24-70 when I stumble upon it - maybe I just was very unlucky and end up as a Tamron user after all.