I have 622 x 25 mm Conti GP 5000 tubed tires. I generally use 100 psi front and 115-120 rear. I tried running lower, but I was both slower and felt more tired in my legs. Not to mention a few bridges I go over would have me pinch flatting where the asphalt of the road is lower than the concrete approach to the bridge.
I actually kept track of my rides and took the six best times out of 12 rides for each different pressure and the higher pressures had the best times and the perceived effort of them was easier.
My suggestion is to keep track of your data and pressures and do your own trials to figure out what works best for your normal ride conditions. When I ride bumpier than normal roads, I do lower the PSI in my tires.
And of course there is a chance my pressure gauge is off. But do you know for sure yours isn't also off?