well we all seem to have one thing in common, we all think the shots should be as close as possible.
of course you can kill at 50, 60, even 70+ yards. the keyword is can. your chances of hiting a bird with enough kenetic energy, amount of pelets, and where it all hits. one pellet can kill if it hits a bird in the head (of course other places as well). but what are the chances you can get the bird to fly into your one pelet!
i agree that the reasonable range is 40-45 yards. any more than that and you need to know the patterning of your gun at the different distances, in varying weather conditions, with the gun and choke you will shoot, and the best possible load for all the variations. then there is the practice, practice, practice.
if you take the time to do all this, take the longershots. otherwise, it is skybusting!