I'm not sure if you guys noticed this.
When I'm using 91 (Shell & Esso) I notice 'stutter' from the exhaust.
While cruising, raise your RPM to about 3k, just cruise until the RPM drops to 1k~1500 without putting the gear to the neutral.
At around 1k ~ 1500 I hear this 'stutter' meaning the exhaust does not produce uniform sound.
When I switch to Sunoco's Ultra 94 this 'stutter' is gone.
Anybody noticed this?