The BigTime Pearl, being a low-load particle and having lower RG and higher diffrential, would basically make this ball earlier and stronger. I've only thrown the Clean and all I can say is that this ball gold on medium-lite oil patterns. I believe that the Clean would be a good step down given the the two were drilled quite differently. You could probably get an almost identical reaction by drilling the BTP weak with a strong backend and a Clean stronger. But I'm no expert in drillings...
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So many bowling balls...So little time.