Even though I believe the RAIII was not available on the Tempest and its derivatives, I feel it would be giving a RAIV a run for its money, if not beat it outright. I would bet it was 300 lbs lighter than a GTO. Keep in mind that the Tempest was a rubber floormat-type of car with little sound-deadener. Meanwhile, the GTO not only was the performance king of the A-bodies, but it was also the most deluxe when it came to appointments.
The GT-37 was not so much an insurance beater as was the incarnation of the stillborn "ET" from the year before. The GT-37 was only fast with the 400-4 engines - the 350-2 was a slug and did not compete with the cosmetic supercars of the day, such as the Rallye 350 and the GS 350, among others.
Here's a link that may be of interest:
GT-37