69% white? They're only off by about seven points; an accurate demographic would likely show Carter up by 4 and Perdue up by 2.
You're expecting the non-white share of November's electorate to be about 38%? You know GA's voting demographics far better than I, but that sounds somewhat high.
The last exit poll data I could find for GA was 2008 where CNN (fwiw) measured the white electorate share as 65% I realize the non-white population (especially Hispanics and Asians) has grown in GA during the last 6 years, but won't minority turnout drop somewhat for a mid-term election, especially among African-Americans without Obama on the ballot?
Still, 69% sounds a bit high. Maybe not impossible for a mid-term, but definitely the realistic ceiling.