Ride the tire at anything under the 65psi listed by the manufacturer unless the loaded bike (with you on it) deforms the tire more than 15% of the tire height or you experience bottoming-out on the rim that causes a flat. There's no need for a rock-hard tire unless you like to be rattled to pieces. Higher-pressures will not make a bike tire roll faster. (Likewise, narrower tires will not make you go faster.)
Ideal tire pressure has a great deal to do with tire width and the bike rider's weight which might also include anything sizeable that might be carried on the bike (backpack, panniers, luggage, heavy items on a bike rack or basket).
Narrow tires require quite high pressures and have a smaller adjustment range for various rider weights. Wide tires, conversely, do not need high pressures for an ideal balance of speed and comfort. "Inflating tires to the maximum pressure recommended by the manufacturer tends to underinflate narrow tires and to overinflate wide tires."*
Folks often overinflate their tires thinking that they'll go much faster and somehow have less drag, when all it really does is provide a harsher ride. Pick a pressure that allows some deformity to the tire (about 15% horizontal drop in the height of the tire if you want to be really fussy) when you are in loaded/riding position. Enough pressure to prevent the tire from bottoming out or causing pinch flats. (Generally, old tires that are worn thin or improper/lack of rimstrip is often a more common cause of those types of flats.)
Some very thorough independent testing resulted in saying "with great certainy that increasing your tire pressure (beyond a certain point) does not make your bike faster on road surfaces that range from very rough to very smooth. In fact, on very rough road surfaces, higher pressures are a lot slower than lower pressures, because the suspension losses are so great. On most surfaces, tire pressure (beyond a certain point) simply doesn’t make a difference in speed."
*This and other technical details provided by a Bicycle Quarterly Article:
Don't ride around on rock-hard tires - unless you absolutely must because your tires are too skinny and/or your load is too large. Many people would be better off riding much larger, better quality tires with supple casings.