I agree you will not find evidence mobil 1 will done internal testing there lab that mobil 1 ep will more shear stable and resistance to heat and because better additive package and base oil it perfomance better some testing benchmarks . So they will go with better and best ,exceed and star ratings because all variables and not all engine same effect on oil when in used .You would not, just as you would not find any evidence that Mobil1 EP will protect engine any better for less than 10k OCI.