When you say "meaningful difference", I am assuming that you are referring to braking distance since that is the primary metric to measure braking performance. Since the brake rotor simply acts as a surface for the brake pad to grip onto to slow down a moving vehicle, I would agree that there should be no performance difference (e.g. stopping distance) between rotors that are made of the same material, assuming the same brake pads, equal quality of construction and street use. While most rotors are constructed of steel, I do not think the coefficient of friction varies significantly between the various grades of steel used. Any performance differences in fade, cooling, etc. would be due to design, mass, etc. Things like brake warping, out of round, etc. are quality issues outside the scope of this discussion. Other issues like brake squeal are probably more dependent upon the brake pad used, vice the rotor.
Last edited by Fudman; 05-27-2011 at 06:49 AM.