Don't count on the temps on the AT 'only' getting down to 30 at night in April. A friend of mine experienced temps in the teens in April last year (granted that was in VA, not GA, but the GA mountains are a lot colder than the flatlands). You never know when a freak cold snap can happen.
However, in 2006 I hiked GA in April during a freak warm spell and temps got as high as 90 in the day, maybe 60's at night. It's really hard to predict what April in the mountains will bring, especially if you factor in wind chill and many shelters/established camp sites on the AT in Georgia experience significant wind that time of year.
Most AT thru hikers will use a 20 degree bag if they start in March/April. The Campmor bag is fairly heavy, but a lot of folks on a budget rave about it, and agree the rating is about right.
My suggestion would be to go with a well-rated 20 degree bag and add layers if it's colder than expected, or use it 'quilt' style if warmer. A pair of long john pants and shorts make a good sleeping combo - you can use either or both depending on conditions.