Somewhere, recently, that article and the test graphs were reprinted on the 'Net. As William stated, the best configuration was actually to only have the front spoiler. This makes perfect sense when you think of the relatively blunt front nose of the 1st gen Camaro. A lot of air gets packed into the engine compartment and under the car once you get much above 70-80 mph, creating a significant amount of front end lift. Adding the rear spoiler adds downforce to the rear at the expense of creating additional front end lift (same problem as the GTO rear spoiler only).
Consequently, for the best handling characteristics, the article showed that this would be accomplished by adding only the front spoiler and leaving the rear spoiler off of the car. However, esthetically, both spoilers definitely look better than front only.
