Let me just say up front that I haven't had to go through what you are facing, but I think it's reasonable for you to think about the possible concerns related to moving...and I do have some thoughts (take them as advice from someone who has NOT been there!).
I would start by thinking about what factors are most important to the overall wellbeing of your child. For example, a good relationship with parents who are able to be present physically and emotionally (because they're not stressed out by lengthy commutes, or work that is an unduly poor fit for their skills and passions). A perfect educational fit. A best friend (keeping in mind that 5 yo best friends may or may not continue into adulthood--and THEY move away sometimes).
And remember also that, as important as school and friends are, the world of a small child generally revolves around his family. I guess what I'm trying to get at is that, often, "your needs" are very significant to "your child's needs". If your family moves to a living or working situation that causes unreasonable stress for you and/or your spouse, that will cause distress to your child as well, which may supercede any benefit to be gained from school fit or best friend relationships. The adults are not necessarily being selfish, in thinking of meeting adult needs, because so much of a small child's happiness depends on his adults'.
