Doesn't the 12C50x run down to 3.something volts?  Increase your
"battery life" by using a 3.something + epsilon regulator instead
of aiming at 5V.  Of course, that'll be more expensive than the
ubiquitous 5V regulators (which tend to be cheaper in the 1A TO220
cases than in the Lower power to-92 cases, anyway, at least from
many of the "hobbyist" suppliers.  A similar argument applies to
zener regulators (of the parallel sort, anyway.)

BillW