Before you put your new "good" pads in, buy a cheap set of organic pads and run them for a thousand miles or so. After that, scuff the rotor lightly, clean it well, and install your fresh semi-metalic pads. This will help burn the oil and such out of the new rotors. I usually only bother with this on the fronts, but after doing it, it seems to enhance braking performance.

1970 Plymouth 'Cuda #'s 440-6(block in storage)currently 493" 6 pack, Shaker, 5 speed Passon, 4.10's
1968 Plymouth Barracuda Convertible 408 Magnum EFI with 4 speed automatic overdrive, 3800 stall lock-up converter and 4.30's (closest thing to an automatic 5 speed going)