For me, 15-85mm on 7D is very useful for walkabout. I used to have a 24-105mm on 7D but 24mm on 1.6X crop (equivalent to 38mm on FF) is simply not wide enough for me. I used this combination on my recent trip and the 15-85mm was used for 90% of my shots. If I need f2.8, I simply change to my...