I have a Southbend with SMF in mine. Yes is does rattle, but I dont see why its an issue?
A stage 2 friction plate was fitted when my Stage 3 was installed(!), but that started slipping after 2 years, so changed to a stage 4 metallic friction plate. Tad more aggressive but not an issue at all.
I tried two newer Cupra's with a Sachs and a helix I think, and I am sure the pedal was ligher on mine.
EDIT: looking at soundbend's now, looks like they have changed the 'stage' numbers. I am sure Stage 4 uesd to be 400something ftlb