The 1991 eagles led the NFL in both run and pass defence
Just because a team used 4 down linemen doesn't mean they are a real 4-3 defense. I could easily argue that several of the Bears, Ravens and Eagles linebackers you reference could actually be considered extra d-linemen not lb'ers.
Over 5500 posts, advanced member, joined March 2002. 1st post (as anonymous) was the day after Super Bowl 35