Karen, I work with pearls quite often, and find it a simple matter to
enlarge holes with the appropriately sized bit in the flexshaft.
Reaming is better left for stone beads and the like. Lubricate the
bit with a little beeswax and holding the pearl with your fingers,
drill, removing the bit to remove debris and to cut down on heat
buildup. I do not find it necessary to either use a diamond bit, or
to drill with the pearl in water, or to dip the bit into water, and
have never done any heat damage to the pearls. HTH.