I go along with the notion of fixed focal length for weddings more so if you have two bodies.. However one exception would be for L series and the 17-40mm would be needed for many group shots where anything more than 28mm would not be wide enough.. Bearing in mind you will be getting paid for the most important day for your prospective clients, the cost will be easily made up for

Danny O'Byrne  http://www.digitalartzone.co.uk/

"All the technique in the world doesn't compensate for the inability to notice" Eliott Erwitt