A 4th gen will actually sustain noticeable physical damage to it's bumper since mine was a decent smack but the unpainted valences flex pretty well compared the bumpers (which most are painted) on a 4th gens. It'll be more than just a bruising.
Hey,see if anybody would be even willing to try that obstacle in their stock (bigger tires ok) 4th gen then lets go up there (Slaughterhouse near Bailey) and I'll get a vid.
Good thing I don't have a painted bumper and any lower approach angle would've caught the rock solidly but I guess physically a 4th gen could make it but at a cost.