I have Both the 17-40 and 24-70 both L so you will not be disappointed in quality the 24-70 is a perfect portrait lens a bit unusual in the the widest angle is at the longest Zoom so the reverse of the usual.. Cant see a lot of point in IS at 2.8  but the lens is quite a lump around same size and weight as the 24-105mm which is also a fine lens and a bit less than the 24-70mm

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

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