Well of course, overinflation should depend on the quality of the tires/tubes. If you have good tubes ( fairly new, not overly patched ), and quality tires that are in good condition ( sidewalls not weather checked and cracking ), overinflating them from 10% to 15% should be fine. I usually run Continential tubes and tires, size 700x32c, rated at 70 PSI. I usually run the back tire at 82 to 84 PSI and the front tire at 80 PSI. I'm 5' 11" and weigh in at 200 pounds. usually the air pressure indications on the side of a bicycle tire are there to "protect" the tire manufacturer against lawsuits. High pressure tires usually tend to lose air pressure over time. The narrow road tires of 110 to 120 PSI tires will lose more air pressure more quickly than the wider sized lower pressure tires you are discussing. My tubes/tires will hold near the 80+ PSI pressure for about a week before dropping down towards the recommended maximum of 70 PSI. I'll usually air them up where I want every 10 days or so. You're certainly right about the higher pressures have less rolling resistance.