I dont have the sliders for the JK (yet) but I do have the brawler rear bumper and I can tell you its tough. I was droping off a huge ledge two weeks ago and lost traction slaming the bumper down on the ledge. When I landed the back tires were almost a foot off the ground. All it did was knock some of the paint off, didnt dent it at all.
I would hate to see what a hit like that would do to the stock bumper.