I can't answer that but I've owned both, used them on a few different bodies & prefer & kept the 16-36 F 4 L IS in particular for it's better images edge to edge. Way back when I started the change to digital from film I had a 20D and bought the 17-40 and I also bought the first version (and an early 1 at that) of the Sigma 18-200 & frankly the Sigma was so close in the range they both covered that I couldn't tell which I used & nor could others most of the time.
"16-35 worth the difference at $1100 ?"
No, it is not. In real use I doubt you can tell or see any big difference. Let alone a "grand" difference!
Keep in mind most people that do see differences are looking for them. Most people don't look for them.