I did some research. Please check my math and history, I THINK they are correct:
Steelers 1933-2013= 80 yrs, no NFL championships, 6 Super Bowls: 6/80= 7.5% championship efficiency
Baltimore Colts 1952-1983 and Baltimore Ravens 1996-2013 for a total of 48 years,
2 NFL championships and 3 Super Bowls between them: 5/48 = 10.4% championship efficiency
Washington Redskins 1937-2013= 76 years, 2 NFL championships, 3 Super Bowls, 5/76= 6.6% championship efficiency
If you just look at the age of the Ravens franchise and championships, we're 2/17= 11.8% championship efficiency.
Looks like we're ahead!
[And of course, I did not count the Canadian Football League championship and the USFL championship we won]