The upper limit to tyre pressure has little to do with the tyre itself but with the structural integrity of the rim. In the workshop we fully inflate the tyres of particularly cheap bikes before we set-up the brakes because the side walls can flex enough after inflation to actually jam the brakes on. Although it's common knowledge that under inflated tyres have higher rolling resistance there is some evidence which suggests that above a certain pressure, depending on the tyre, rolling resistance actually increases because the tyre can't flex over bumps.
I find 100psi front and 110psi rear to be a good compromise between comfort and speed.
