Came across this link that might be helpful to anyone tossing up between the Canon 16-35 & 17-40 lenses http://www.luminous-landscape.com/re...on-17-40.shtml.
I was tossing up before I bought my 17-40 and in the end it was mostly landscape value I was looking for where there was a likelihood of longer exposures over a tripod. Value for money and moderate use of a smaller f/stop toward the wider end helped sway my decision.
Hope others find this useful