Just anecdotal experience…but I recently did the 62 mile Barry Roubaix race. I’m 190lbs, had 40mm tires, ran 40psi in them, tubes. My impression was it was WAY too high. If I did it over again, I would have tried something 30-35 psi. It was fairly tame gravel. I really don’t think pinch flats are all that great a concern unless the gravel is pretty chopped up with potholes. And even then…you’re not going to have sharp edges like you do with asphalt. For what it’s worth, I race cyclocross on 35mm tires at under 35psi, and have never had a flat.
It was a pretty jittery ride the whole time in the gravel race. Back ended up being pretty sore the last 20 miles. With the amount of vibration and bouncing I felt the whole time, I’m pretty confident lower pressure would have been faster too. I ran the higher pressure because a decent portion of the race was on asphalt…but realistically, lower pressure would not have harmed me. Being a bit on the bigger side, I was passing people on downhill asphalt sections without pedaling anyway…I could have given up a few watts and just tucked in behind people on the pavement.