I swear on my life I can feel the difference when the T-Tops are off. It just doesn't feel quite as fast. Obviously with all the air entering the car.

 

I've seen those Motortrend and Car and Driver runs in the 1/4 where it was SS vs WS6. The WS6 would "most" of the magazines trap a little higher in the 1/4 mile. I think its just the better design ram air on the WS6. That would be the only reason it would outrun an SS. Like everyone else has said. An LT1 is an LT1, and LS1 is an LS1 regaurdless if its in a Camaro or Firebird.

As for underrating. LS1's are most of the time indeed underrated. They usually dyno 300+rwhp stock except some of the weaker ones. LT1's usually dyno around 240+rwhp with some occasional weaker ones like LS1's. Mine dynoed 255rwhp stock. With adding the 15% drivetrain loss that would put me at 293fwhp which is rated 275fwhp from factory (is which of course what the factory rates them at). So sometimes the LT1's are indeed underrated also.