I would recommend at least 35psi as that is Toyota's recommendation for highway usage.

Running higher pressures (staying below the max rating) can affect ride, noise, tire wear and handling. However, pressures higher than the car manufaturer's recommendation are not always a problem. Sometimes ride softness/comfort gets the nudge over other factors - witness the orginal 24psi recommendation by Ford for the Explorer and the Firestone tire issue.

I suggest reading Driving Under Pressure for a glimpse at how higher pressures don't always cause poor handling and bad tire wear. If that link stops working, here is another link to the same article posted on GH

Research issues and keep an open mind