I really enjoyed the review (keep em coming) and am enjoying my 17-40mm f/4L IS. It is light and gets the job done. I used to have the 16-35mm f/2.8L IS II and for the price (even getting it at a bargain used; $1100), I decided to go with the even more reasonably priced 17-40mm I found used on FM.
The results are nearly the same as what I used to get on the 16-35mm, since I would stop it down anyway. The times I used it at f/2.8 the results were not that impressive. Lots of vingetting on both...cannot say the 16-35mm II was so much better in the corners.
So for me, the decision was easy...I don't do weddings and appreciate the lighter weight and 77mm filter size of the 17-40mm. I also like the 5mm on the longer end! 17mm is plenty wide on FF.
Here is a sample that I took with my 17-40mm f/4L IS on a 5D MKIII: