Being trained in the aviation industry, I always use the maximum specified pressure for the car, as placarded on doorjamb, glove box, etc.
We were taught that hydroplaning speed (in knots) is nine times the square root of the tire pressure. (MPH would be knots times 1.15)
More pressure in tires would be safer- to a point. Too much, and you lessen contact area and wear out middle of tread faster.