i've yet to see anyone on here break a set of wheel spacers.
i run the dura blue phenolic (hybrid plastic) style on front of my spare black blaster and haven't had any problems.
i've also seen the stud style run here in this rough terrain with no problems............
Providing the studs are fitted to the wheel hub studs with the addition of Loctite and the lug nuts are tensioned to 33 ft lbs you should have no problems.