I cut 2"ers with my light dudy JBAR some of the bigger ones not sure if there 2 or 3 will dent the deck but cut fine. Not sure what it is rated for, but its a light duty on for sure.
Cleared about 1 acre last fall, (did not have much time) It was cutover and I wish it was only 2 inches, but some were much larger. If there are any you can't push over make sure you cut it off flat with the ground with a chainsaw. And I echo what others have said, "don't backup." I know I am slow, but I planned every cut where I was going to start and where I was going to stop. Once I would get started I would just keep pushing. I have a standard duty bush hog and I did not dent it but I did slip the clutch more than once.
If your not on a time schedule wait until early fall when the leaves are gone makes it alot easier to see things