Run them at or just over (2 psi) the factory's recommended pressures (36 psi front, 30 psi rear) if you have any doubt about them getting you home safely. Those tires have relatively stiff sidewalls and their compound is similar (albeit not quite as sticky) as the OEM RE070's.
Small tire pressure adjustments can dramatically alter a car's handling at the limit. However, for a sane, 300-mile journey at normal speeds on the street, your tires are safe to drive on as long as they are neither under- nor over-inflated.
The ride will be harsher at higher pressures, but higher pressures also equate to better fuel economy due to lower rolling friction. Remember that tire pressure increases after you drive on them (more if you drive harder), and outside temperature can affect pressure as well. A good rule of thumb to follow: for every 10 degree increase in ambient temperature, tire pressure increases 1 psi.