There certainly is a relationship between tire pressure, speed, and comfort. The relationship between pressure and speed is direct and between pressure and comfort is indirect. I bought a recumbent racing trike that came with Schwalbe Ultremo ZX 406 tires. The rated pressure is 85 to 160 PSI. If you run them at the highest pressure, you might as well be running solid rubber tires. The ride is incredibly harsh. The ride is faster though. I dumped them almost immediately for a set of Tioga PowerBlock tires rated at 35 to 80 psi. Much more comfortable at the rated pressure but slower. I don't like running Schwalbe tires much below the maximum pressure because of bad experience with premature sidewall failure. The sidewalls flex more at the lower end of the rated pressure range. It may mean a shorter life for the tire.