As a rule, performance rotors shed heat more effectively. This is important, since the majority of heat generated by braking friction collects in the rotors. When engine mods like an air intake system or a better-breathing exhaust are installed for more power, performance rotors go nicely with a new set of brake pads.
For our purposes within this article, performance rotors we sell are the same diameter as factory ones for easy installation without modifications. (Larger diameter rotors are typically part of "Big Brake Kits", which we'll discuss in Part 2).