* Gear ratios: Different rear-end gear ratios significantly affected top speed. A higher numerical gear ratio (e.g., 3.55:1) would result in a lower top speed than a lower numerical ratio (e.g., 2.73:1).
* Tire size: Slightly different tire sizes could impact the final drive ratio and thus the top speed.
* Weight: Added weight from options or aftermarket modifications would slightly reduce top speed.
* Aerodynamics: While not a major factor at the speeds these cars reached, it still played a small part.
* Road and wind conditions: These are obvious real-world variables.
* Engine tune: Variations in engine tuning and condition influenced the car's power output.
While some sources might claim a specific top speed, it's more accurate to say that a 1965 Pontiac GTO 428 with a relatively low rear-end gear ratio could reach speeds in the 120-130 mph range under ideal conditions. However, reaching those speeds would have been risky and likely involved exceeding the car's designed operational limits.
