I have run it on mud, gravel, grass, wood chippings, mulch, concrete and a disused rail way line. I've even hucked it off jumps into must if those surfaces. The XL is still running like a dream. Behaves wonderfully at slow and high speed.
Currently I'm running on pairs of Max Amps 3s 6000XLmAH True 100c. Run times vary between 28-45 minutes (depending on how you drive)
I has been run completely stock, in order to review it fully and fairly. I haven't had any issues with the battery trays, or it bottoming out. The front arms are incredibly strong, contrary to what everyone seems to think.
You do get some torque twist if you try to snap the throttle open from standing (like any high power rig), however it's easy to handle. The steering really gives you great accuracy, the rear end is planted and delivers power without being skittish.
(I am aware that my choice of battery is beyond many peoples budget, and other high output batteries are available.)