On my Toyota Mini-Truck with 33-10.50 tires I rarely go below 19 psi, and run 30 psi on the street. Experience has shown there's no need to go lower with that particular combo in where I go. With the 'glass dune buggy my street pressure was 10 psi. When we got into really, really soft stuff I'd go clear down to 8 psi (I think that I did that twice in nearly 20 years). I know a guy who routinely runs his Sami on 35's w/o the valve stem cores in. He goes into a lot gnarlier trails (Rubicon, Hammer's, etc.) than I do. He also runs a tire that I would never, ever run on pavement (one of the ungodly heavy Super Swamper variants).
Even though I can't wrap it in a scientific explanation my rule of thumb is full pressure if I'm going fast, lower pressure if I'm going slower. The exception is long washboard (Saline, El Arco, Barcroft Station, etc.). Again, experience has shown me (desert races over the last 1.5 decades, Baja, NV/OR Great Basin, Mojave Desert, etc.) that this is what works for me. I make no claim that it will work for anyone else. I don't even, yet, know if it will work for the CTD as I don't yet have enough experience with it to know for sure. I suspect that it will, mostly because going fast is hard on equipment and we'll be going slower since I've no desire to beat up the camper.