I got to throw both balls back-to-back the other day at a Storm/Rotogrip Open House.  I threw my own Gravity Shift (that actually fits my hand well) against one of the demo Cell Pearls (that doesn't fit my hand quite as well), so take these results for what you will.  Both had similar drills, pin over ring finger, just shy of being centered over the bridge, MB just right of the thumbhole, no x-hole.  The Cell Pearl was about two feet longer, and about three boards stronger on the backend.