My only fear is our recent performance against rookie or 2nd string QB's.

This is actually kind of a myth, or only half right. The Saints (at least under Gregg Williams) didn't actually struggle against rookie or 2nd string QB's that much. They really only struggled when the QB that they faced in the game was not the one they expected to play during the week. The Rams and the Titans games last year. One changed QBs during the game itself, and the other, Sam Bradford was practicing for the Rams the week before, then decided he couldn't go. Arizona in 2010, Derek Anderson was supposed to be the starter but the Cardinals benched him unexpectedly. Cleveland in 2010, Colt McCoy had only started one game, one week before. The rest of the year had been somebody else.

We all remember they looked extremely terrible against Seattle in the 2010 playoffs, but all week long that week there was a QB controversy, and the starter wasn't announced until Thursday afternoon before the game. In games where the defense absolutely sucked, every one of these teams had some kind of QB controversy or injury, so the QB that was out there on the field was not the one that the team had game planned for.

They actually looked pretty great against young or 2nd string QBs like Matt Stafford or Mark Sanchez in 2009, Painter in Indy, even playing against Cam. Because they were prepared. It's only when people pull the switcheroo at the last minute, that the Saints defense looks really bad, and if you look around the league, almost any team would experience a drop off in their defense if it isn't the QB they prepared and expected to play.

It still sucks to watch it, though!