I routinely run 20-22lbs front and rear when doing long stretches of gravel. On my previous BMW GS, they specifically recommended pressures as low as 16lbs for off road. I assume by they meant slow going.
When doing the Dalton in Alaska and the Old Denaly Highway, I ran the 22 lb set up. Worked great. Didn;t travel much faster than 45-50 and it makes a large difference in stability compared to stock pressures used on the highway.
Of course, I carry a tire inflation device with me and air up before picking up speed on pavement.
Give it a try, you will find it makes off roading much more pleasurable.