my colleague had a 16-35 and i could compare it with my 17-40
he has the benefit of shooting at 16mm vs my 17mm, but his lens distorts buildings much more than mine
and i felt that the difference in price didn't justify the gain of 1mm
so far i'm very happy with my 17-40
Well I would say thats furthest from the truth of difference
.
I too owned both and love my 16-35II, and enjoyed the 17-40L as well, but it doesn't even compare to the same shortness towards centre at all. Big difference.
The biggest thing is the sharpness, next being the 2.8 vs 4 depending on if you need the extra light or not, and then the extra 1mm being minimal to non importance.

(24Lii, sigma 50A, 135L), and for the other ends of the spectrum, sigmaEX 14mm2.8 and sigmaEX 100-300F4.
. Neither of there lenses is as good as the 24-70mm II. Which I find covers an ideal range for landscapes. And it has fantastic sun star effects with lights. If there is only one lens to have its the 24-70mm Its so versatile. 
