When the toughest conference from top to bottom has matched up with other top conferences, it has not performed well. SEC teams went 4-6 against the ACC, 1-1 against the Pac-10 and Big East, and 0-1 against the Big 12. The SEC and Big Ten did not play once this year, so overall they are 6-9 with a 0-2-2 record against the other BCS conferences.
I know that the ACC is really the only conference who has enough games to claim any kind of bragging rights. The Big 12 only had one game, and it was a good team against a bad team, but 0-2-2 is the actual record no matter what the reasons.
The SEC has allowed 22 points against BCS conferences: not bad defense, but not stellar either.
If you look at all nine losses, the SEC gave up 290 points, 32.2 points per game, and scored 159, 17.6 points a game, a 14.7 margin of victory. If you look at all 15 games against BCS conferences, the SEC outscored all BCS opponents 354-330. Against BCS conferences in total they have allowed 22 points.
The 6-9 record against the BCS conferences means the SEC has been beaten 60 percent of the time when they have stepped out of conference.
While some may argue that most of these are lower tier teams, some of them are second and third place teams in their divisions, and the bottom two teams, Kentucky and Miss. State, are 1-1, so you can't lie the blame at their feet.
The stats do not bode well for SEC fans claiming that it is the toughest conference top to bottom. The scoring defense numbers show that when they have stepped out of conference this year their defense has not been near as good, but the season is not over yet, and based on recent bowl performance the SEC should do well.
However, to this point in this season, the SEC has not proved it is the dominant defensive conference, yet.