For what it's worth, I have always run regular, wether it was in my 1988 mustang 5.0 or my 1989 nissan sentra. Of course I had the inevitable guilt attack and tried premium in the stang, no difference.
My Nissan has 180,000 miles (just turned yesterday) and runs as well today as when it was new. The motor has never been opened.
As I read through this post I saw little evidence that regular adversly effects my vehicle.
As I understand, techs please help, the computer will take care of adjusting fuel, air mixture to compensate and manage the performance of the motor.
I did read where regular can negatively impact the cat-converter?
As I think most agree the most important additive you can put in your car is clean oil every 3 months or 3000 miles (not sure why 3 months?)