I wouldn't look down too much on the kit lens you have... the MTF charts on this lens appears to be nearly as good if not better than L lenses at this range, however, other factors such as construction/sealing/durability tip the scales in the L lenses favor. You've got a nice piece of equipment and heads and shoulders better than its original 28-135 lens. Learn your gear. I heard one seasoned pro say that when he gets new lenses, he would play non stop with that lens/camera for 6 months to a year (minus other photoshoots that may need other equipment) so that when he was done with that period he was confident he knew everything about that gear so when situations popped up in which he needed to use that gear, he would know not only what f-stops worked best for what he wanted to produce, but where was the sweet spot in the lens, in what conditions the gear worked best so he can get the best shots when he wanted it. This is a lost art now-a-days where people dont get as intimate with their equipment and dont learn it good enough, and when they get missed shots, they blame the gear, not themselves.