I believe Powerstop is a respected brand but have no experience directly. Others can chime in.
Is K6931 the kit with slotted/drilled rotors and carbon/ceramic pads?
I'll express my opinion about drilled rotors.
IMO, Drilled rotors are one of the last things to consider, after everything else has been done including fully flushing the system with high-boiling point fluid, use of high carbon steel rotors and the best pads you can find, braided stainless hoses, replace all hardware kits and hyper-anal meticulous cleaning and assembly of all parts.
Rotors are drilled to increase surface area and thereby increase cooling. The downside is that it also reduces mass and therefor, the amount of heat a rotor is able to absorb. More mass = ability to stop harder and stop more often before the brakes fade. Keep in mind that race cars have massive rotors to begin with and so drilling still leaves a lot of mass. Race cars also have cooling ducts which direct fresh air to the brakes. I think for most street cars with small-ish rotors and no cooling ducts, drilling probably reduces performance. I've no numbers to prove this but that is what I suspect.
Drilled rotors sometimes experience cracking around the holes. I don't know if manufacturers have fixed this since I first read about it but it is a concern of mine. As an example, Porsche doesn't drill their rotors but casts their blanks with holes. The holes are then finished with the rotor surface. This is done to prevent cracking but it raises cost. Porsche rotors can be $1500 each.
Everyone is free to do what they want and drilled rotors look killer. I however, would focus on
1) flush with good quality, high-boiling point fluid such as Motul RBF 600 or ATE 200
2) Use high-carbon steel rotors. "High Carbon" is a grade of steel. Call or email the manufacturer and ask what their rotors are made of. If they say "Gray iron" or some other grade then it isn't high carbon.
3) New hardware kits and meticulous assembly. Don't forget to scrub the rust off the hub to rotor mating surface with a wire brush.
Consider using a slotted rotor if you are using an aggressive pad. I don't consider ceramic to be aggressive. Slotting helps to move dust and gasses away from the friction surface and removes negligible mass. I'd rather have a high-carbon steel rotor with no slots than grey iron rotor with slots.
The DBA rotors on my car have heat paint which turns white when a predetermined temperature is reached. The heat paint is visible on the edge of the rotor in the photo below. Green is the coolest at 458°C/856°F. Normal street driving in my car has not even triggered this to turn white. They've never reached a temperature which triggers any of the heat paint. The point here is that the rotors aren't getting hot enough where drilling will be a benefit. They are cooling perfectly on their own without holes.
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