A lot of people say the Sigma is razor sharp. It just isn't nearly as sharp as my 70-200L. It is only as good as my 50 1.4. Don't get me wrong. I think it's not bad. It's just not as sharp as I was hoping. Things look nice on LCD but come out slightly disappointing on monitor. Its AF seems slow too, not as snappy as I wanted. I've never used the 35L so I can't compare. Am I expecting too much? After all, a wide angle is more difficult to make than a tele. Do people really sell their 35L to get this? Well, maybe I have a bad copy...
i would say my sigma 1.4 is as sharp as my 2 copies of 70-200 mk2 at 1.4 vs the zoom at 2.8
by f2 to f2.8 its way sharper
but they are very different lenses with different characteristics