We've struggled with whether to move, and gave ourselves a self-imposed deadline of before the oldest starts 5th grade, with our rationale being that this would give him 1 year in the new elementary school to make friends before starting middle school. He's in fourth grade now, so we've got less than a year to do it, and it's looking less and less likely. Both my wife and I moved multiple times during childhood, and while I think we turned out alright, we wanted to avoid that for our kids. However, the converse is that I think an argument could be made that there are just as many negatives to keeping your kids in the same community with the same kids and friends for their first 18 years.
Just to stir things up a bit, I often question why my wife and I, and everyone around us, seem to place such a high priority on the kids. My parent's certainly made some decisions with my brother and I in mind, but I guarantee they probably never had such in-depth discussions weighing all the pros and cons. Education is important to us, and we've got our kids in one of the top public school districts in the state, and this is one of the major reasons we live where we live. But then I look at where my parents moved us right before I started high school, and they clearly did not concern themselves TOO much with that.
So I understand your dilemma, it's similar to ours, and while I haven't figured out how to move past it, I also feel like maybe even asking this question of ourselves is really a mistake.