Factory recommends a 3psi bump in the tires for extended high speed driving.
"If you are operating your ST vehicle in areas that allow high-speed driving over 100 mph (161 km/h), increase the tire pressure in all four tires by 3 psi above the pressures listed on the Tire Pressure placard located on the driver?s side b-pillar."
So although 3 extra PSI is probably fine for road trips, it's not really necessary unless you're REALLY speeding.