For wedding and event photography there is no doubt f/2.8 is the way to go if your shooting style revolves around low light without flash. IMO sell off your 17-40 and 24-105 and pick up a Tokina 11-16 and a EF-S 17-55 or 24-70. Or, for $400-500 less than the 16-35, add both a Tokina 11-16 and a Tamron 28-75 and keep your existing lenses. It's not worth the cost for a 16-35 for use on a crop body only--you are paying a premium for the range of a lens which you will not use. However, if you are planning on FF in the near future considering the 16-35 isn't that bad of an idea. You may also want to seriously consider picking up some prime lenses, something along the lines of a Sigma 30/1.4, Canon/Sigma 50/1.4, or a EF 85/1.8.


-Matt