Our trip is over and the X5 held up remarkably well! No issues on the trails for two days of rocks and mud. There were a few instances of "send it with lots of power" which lead to some good subframe whacks. She held up and was able to drive home at highway speeds with the (recharged) A/C blasting.
With real tires, not these Walmart "Black Lion" specials, I think it'd do even better off-road.