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If you want good LS400 pads, just get custom ones made from Carbotech or Porterfield. They're not really that expensive compared to other high quality pads. Call them up, get almost any compound you want.
I talked to porterfield a few months ago about making pads for LS calipers when I was there picking up pads for my other car. They can custom make any track compound I want, but they can't make street pads other than the r4s.