UGA Sagarin Predictor = 92.59
GT Sagarin Predictor = 76.43
Home Advantage = 3.52
Estimated point spread = 92.59+3.52-76.43 = 19.68
Ref.
http://www.usatoday.com/sports/ncaaf/sagarin/
From a Phil Steele article, when the spread is between 17.5 and 24 points, the underdog wins 6.76% of the time. When the spread is between 14.5 and 17 points, the underdog wins 13.16% of the time. Setting the %chance at the midpoint of the point spread range, and interpolating, in a 19.68 point spread, the underdog would win about 8% of the time.
Ref.
http://www.philsteele.com/blogs/2012/Aug12/DBAug1.html