Growing up in Oregon, a lot of our "off-roading" was done on old logging roads.
The best way to deal with downed trees? Grab your chainsaw, cut it, winch it out of the way for everyone else. Of course, some of the trees there are too big to deal with any other way, especially in our 1960 CJ.
No saw? Going over at an angle will reduce the chances to high center. Same thing as you do with ditches.