The "Mud" tires that are commonly available now a days are glorified street tires that help when in muddy conditions. True mud tires have a much greater void ratio in the tread. Swampers, gumbo monster mudders, ground hawgs, SImex etc.. Those tires are poor on the street but dig in the mud like you would not believe.
You are putting way too much thought into the load range of a tire. You mention swampers as your first choice, however the sidewalls are much stiffer due to the bias ply design than a typical radial is regardless of the load range (I'm not aware of any load range E radial that will not have a sidewall bulge at 5 psi unless it's not mounted on a truck). Pressure is your friend. The lower in the sand, the better. At high pressures, all gravel roads suck.
A lot of the factory wheels have a "bigger" safety bead. 8 psi in the sand is probably fine, in the rocks that's pretty low without beadlocks. I generally run about 10 to 12 on my 60 and basically let the 40's air down till the "wiggle" a lot when kicked. Generally, starting at 15 and then seeing how low you can go from there works fine. Very few rims will pop a bead at 15 psi.
What size tires did you buy after all?
