comet 20 series driver

Hi everybody, I have 2 comet drivers. one has steel weights, the other has zinc or aluminum. is one better than the other? or
do they engage at a different RPM? Or is there no difference? I recently got a set of lower RPM engagement springs. Im trying to
lower the engagement off idle, Im running stock springs now, and keep popping the front end up. 5HP big block. speedway greenhorn, street legal.