I just discussed this with some PHs in South Africa, where the Toyota land cruiser is the ideal bush vehicle, and these things are tested off road in real conditions daily. They endorsed the use of the aluminum skid plates. I think that the strength is also an exponential function of thickness, so while aluminum is 1/3 the strength, so if it's twice as thick, it's 4 times as strong. I might be wrong about the math of it, but I am going to get a set of plates and we will see how it goes.
600% thicker for twice the strength or 300% for the same strength, assuming the 1/3 strength figure is correct, of course.