For those of you that have been doing this longer than me (which means most of you), I need some help with lenses. Currently I have a 40d with a 24-105 f/4L as my only lens. I am looking to get either the 70-200mm F/4L IS or the 70-200mm F/2.8L non IS. The cost of the lenses is very close to being the same on B&H, so I am really looking to figure out if being able to shoot at f/2.8 is worth not having IS. I am also wonder (no matter which 70-200 I go with) if I should change my primary lens to something like the 17-55 f/2.8 or should I keep the 24-105. I almost feel like if I keep the 24-105 it and the 70-200 overlap a little too much .I could be wrong. To help you, I generally enjoy shooting candids, outdoor portraits and some landscape. I am not by any means doing this for a living, but I do get asked from time to time to take pictures of friends and family members, mainly for fun. Thanks for the help!