Third Gen. Firebirds and Camaros seem to be better aero wise then the later 2003 up models.
Lot of them have gone fast, Raines, Kugel etc.
J Y/B
Unless you are very acquainted with those two cars, I would not be making a general statement about the "aero safety" of 3rd Gens at speeds above 230.
Just by reading various articles -- one can find out a lot about them and the lots and lots of things that were far from stock.