It still stands up to the best 35mm prime. And sure the Canon is a stellar lens, and renowned for its consistency and control of artifacts. I hope its sharpness comes out whenever Canon releases new sensored bodies. Hopefully for Photokina. But for today, the oddly flawed 24-7/4 is amazing at 35mm. I am most disappointed by this lenses' inconsistencies, but now knowing its strengths, I am going to keep it. There is an awful lot to be said for a consistent zoom.
I lust after the 24-70/2.8L II a bit, but it's hard to imagine picking up that lens today when Tamron offers a stabilized version for half the price, that's better than every other fast full-frame DSLR standard zoom on the market except the lofty Canon, and that Sigma is most likely preparing their 'Art' replacement that will also likely bring OS to the range, along with the constant rumors that Canon has a stabilized update of their own in the works.
I'll probably pick up the Tamron, though. It's hard to pass up versatility and frugality in a single well-rounded package.
Also, if you look at the field maps at DxO, while the FE24-70/4 does indeed look pretty good at 35/4, it only approaches the 35 Art at f/4 in one little dot in the very center, and is slightly (and I do mean slightly) behind across the image as a whole. Not a big deal of course, but I do like to keep my comparisons straight