The old ACC with nine teams was the perfect conference. This was back in the 11 game season days; 8 conference and 3 OOC. No need for a CCG, because Florida State won the league every year anyway.
Since we play 12 games a year now, you could play 9 league games and still do 3 OOC, and at least one of those should be a comparable team.
But there is absolutely no reason that two teams should go 10 years without playing each other, no matter how big the conference.