In 64 and 65 the GTO was the most sought after cars you could buy. It also was a very quick stock street car. The other makes played catch up once Pontiac came out with the GTO and yes by 1968 they were faster cars from the factory. In 64 and 65 the GTO was at the top, for a Factory car.
I owned 65 in 1965 and with single carb I remember outrunning friends in their 63.5 427 sideoiler Galaxy and the 390 Fairlane. Remember this was a family car not a 2 seater like the vette and cobra. I also had a 65 FI vette and a 62 260cube Cobra and they were no quicker then the early GTO. I saw 427 63 z11 cars and stage Mopars with aluminum front ends that may have been a little quicker in the early 60s but they were special order cars. People like Royal Pontiac were showing everyone how to do a "super tune" on the Goat and those cars were in the mid 12s
Pontiac started the whole Muscle car race so give them credit.
Do you remember the "swiss cheese" cars, aka:factory lightweight cats????