There are various recommended presure charts -- like this one from Michelin -- based on weight combo. But you also need to take into consideration road surface.

Generally, you'll go faster on surfaces like chipseal with lower pressure. Even major manufacurers have recently concurred that "Wider tires roll easier, yield higher mileage and offer more comfort and grip" ~Continental, and are offering more choice in performance tires.

And this is true. Tire construction is the greatest arbiter of comfort and speed, not pressure, though any overinflated tire exerts a negative effect on both.