I have to disagree with that your putting new parts on used parts when you change your pads you should change your rotors.

 

 

This is the way on German cars.....my wife's uncle is a tech in Munich. He said he feels it's "OK" to change pads only in the USA, provided the rotors are within spec (thickness and runout). He said in Germany they change both, because they are doing 250km/hr to 0 r
epeated stops in daily driving, and they tend to have semi metallic pads as well....my .02

p.s. I have experimented on the BMW, where the rear brakes started to squeal as early as 20k. Everyone say no way to cure except replace the rear pads even though only 25% worn. To take rotors out of the pic, I changed the rear pads only, with new OE pads. sure enough, noise gone. Real downside of semi metallic, as well as the tons of dust...also interesting how the rears wear so much faster than fronts, defies physics (but not ABS and DSC and traction control)

 

I can only give ya my experience in 300k miles driving 2 LS's when I used old rotors which did not pulsate was never sorry and I always felt braking was excellent. My buddy who is a retired Toyota master tech agreed with me when I said "wow these rotors are bulletproof". I used Lexus pads or Akebono

 

Warm, you can lead a horse to water...