Tire design matters at least as much as pressure. I just replaced a set of Specialized Hemisphere 700x38 tires (recommended 75-100 psi - I usually rode them at 85-90 psi) with Michelin Protek Cross Max 700x40 (36-87 psi - I ride 'em around 70-80 psi), for better flat resistance. The two are much more different than pressure would indicate. The higher pressure Hemispheres have far more flexible sidewalls and ride "softer" and felt faster on pavement without feeling squishy. The Michelins have very stiff sidewalls, rider harder overall but better on unpaved trails and grass.

My actual riding speed isn't significantly different, despite the very different feel to the rides.