That was me, of course, posting in the Track forum.
The RG and differential values should NOT help you pick a ball, but it should help you know more about the ball's reaction, and help the driller drill the ball.
Remember that ball designers, if they are doing their job well, pick the RG and differential for different weights to insure that the ball's reactions do not vary greatly, as the ball goes from 14 to 15 to 16 lbs.
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"None are so blind as those who will not see."