I always feeel so sorry for the kids who move here from the Northeast or Midwest. They get such a short break. Even 90 percent of the private schools have followed the public schools with simliarly early start dates.
First a disclaimer, I don't know much about the areas East of Stone Mountain, so I can't comment on that.
I am going to suggest you start with the city of Decatur. Most school systems in Georgia are county school systems -- that is they serve the entire county. In Metro Atlanta, we have some exceptions (Marietta, Buford, Decatur and Atlanta). Decatur is in DeKalb County but has its' own school system which is very well regarded.
If you go to harrynorman dot com and click on find homes, then choose the function to search by schools, choose high school, then choose Decatur, (not Decatur High School) enter all your other information, you will see some of your choices.
Decatur High is very small by Metro standards Decatur schools are wonderful but you will be paying higher property taxes -- but I bet they will still be lower than where you are coming from.
The key is that you have to stay in the City of Decatur.
The Lakeside or Druid Hills clusters are also probably conveniient, but as a DeKalb County parent, I am concerned that the system is falling apart -- or hasn't hit rock bottom yet. We have a school super. who can't seem to make decisions, or makes poor ones regularly, We can't seem to stay out of the news and our Super. decides it is because one of the local networks is out to get him. We also have a very poor school board, comprised of many members who aren't educated themselves.
http://www.ajc.com/metro/content/metro/dekalb/stories/2007/05/10/clxedboard0510.html (broken link)
Oh, I got distracted -- within Lakeside, there are a lot of elementary schools supported by the community and others which aren't. Within Druid Hills, the best is Fernbank, Briar Vista is wall to wall Montessori and wouldn't be a good place to transfer your kids and well the others need some revitalization.
There are some positives going on in DeKalb, in fairness. We seem to be making progress in the ability to hire decent teachers -- in part because Gwinnett has become so big all those teachers from DeKalb that fled diversity to Gwinnett are begging to come back. Additionally, Gwinnett has become pretty darn diverse.
Onto Gwinnett, I am thinking that perhaps Peachtree Corners might be too far. While the schools are huge, Norcross High has an IB program that is suppose to be great and the middle school has it as well. I know many people who are very happy at Simpson Elementary but it is 1000 students.
Hope this helps.