Sean,
I only have experience on a 1.6 crop (60D). I have a 17-40 that has taken outstanding pictures, but thought the 2.8 would be better. I ordered a 16-35 when they went on sale for $1299 in December, but was disappointed with the IQ compared to the 17-40. I sent it back to B&H and had them send me another one. Although it may have been slightly better than the first copy, it was still not better than the 17-40.

My tests are only my opinion, but what I found was that I needed to stop the 16-35 down to nearly 4 before it was acceptable IQ. Comparing both the 16-35 copies at the same aperture (4) to the 17-40, left me sending the second copy back as well.

My 17-40 was a Canon refurbished, so the price difference was nearly $800. I strongly recommend the 17-40 (at least for a crop sensor camera).

Brian.