First off I have been running Drilled and and Slotted rotors on my Street ( Currently a Magnum and Ram 3500) and race cars for years (Decades). Drilled/slotted rotors make a positive difference (stopping distance). Among other reasons the purpose for the drilling/slotting rotors is for heat dissipation along with dust and gas evacuation generated during braking, there by Increasing friction during braking. As a side benefit the Drilled and slotted rotor mfg's that I have been using (EBS and Powerstop) use a better base material quality and along with the previous mentioned benefits have more than doubled the service life of my braking components. That's an opinion from someone that actually uses them.