The best defense of all time?

The Chicago Bears defense this year has been incredible. The question is: how do they compare against the best defenses of all time? One way to measure this is to look at their points allowed and compare it to the second best defense in the league. For example, the 2005 Bears have allowed 151 points through 14 games. The second best team in the league is the Indianapolis Colts at 206 points allowed. That's a 55-point differential.

The best teams in modern history (last 50 years) by this measure:

If this year's Bears allow 11 points fewer than the Indianapolis Colts allow over the next two weeks, they run up to the top of the list. That would also establish a remarkable defensive tradition in Chicago with three different Bears teams as the best three defenses in modern history. And, despite the anemic offense displayed by this year's Bears, the playoff track record of the other dominating defensive teams bodes well for them.

By the way, all three NFL Champs listed in the chart allowed 12 points or less in their respective championship games:

1985 Bears over the New England Patriots 46-10
1963 Bears over the New York Giants 14-10
1965 Packers over the Cleveland Browns 23-12

The 1970 Vikings lost 17-14 to the San Francisco 49ers in the first round of the playoffs.

Going back into ancient times there is one defense that allowed 80 points fewer than the number two defense, the 1949 Philadelphia Eagles, who defeated the Los Angeles Rams in the championship game 14-0.