Matt, I was moved around a lot as a kid due to a broken family and parents bouncing my two sisters and I back and forth. I went to three high schools in three years. I suffered socially because of it and have zero friends from high school as an adult. I missed proms and do not attend the reunions of the school I graduated from because I don't know anybody. Life worked out in the end, but I do wish I'd had a healthy high school experience and the lifelong friends.
I lived in the same town from 3 years old until my last year of middle school when my father left us to gamble, drink, and chase women. My mother moved us and I left behind very close friends. I started high school as a new kid in an area exactly how you described. The kids were well established and most were second or third generation in the area. I struggled and hated my parents because of it. Ended up getting in fights and withdrawing. It was even harder for my little sister who was in 8th grade. She became promiscuous and ended up in a bad crowd.
With that said, I don't think it has to end up as badly as it did for us. My mother was not supportive or even involved in our lives after the move. She was struggling to survive on her own and working two jobs. You, on the other hand, have an intact family and a strong sense of good parenting. Your kids have a family circle to feel secure within and to draw a sense of belonging and love from. You also have the financial means to start your kids off in a new social environment in good after school programs and sports...where they quickly meet the good kids with similar interests and involved parents.
Moves in and after middle school are the most difficult on kids, but much harder on girls than boys. Read "Reviving Ophelia" by Mary Pipher
Obviously the younger kids are the easier they adjust to a new environment. If your going to do it, now is the time.
When my ex-wife remarried she moved my daughter to AZ (despite my legal efforts to stop it). My daughter was in 10th grade. She struggled meeting new friends (Girls are vicious) and moved back with me in CA a year later lonely and troubled (a therapist gave me Reviving Ophelia). She's 30 now, happy, married, and gave me a grandson, but she calls herself a "nomad" when asked where she's from and has very few friends.
Now that I'm nearing 60, retired, can look back on how short the time is when we actually can influence our kids life and phycological security, and how quickly if flies by, I would have made more sacrifices to assure my daughter's life was stable until she left for college. ...even suffering through six more years with her control freak mother. Once they are out of high school their form is solid. There's still plenty of time for us to change direction after the most influential parenting time is finished.