Hi Colin,
Well that's quite amazing how you can tell what the leakage is for each capacitor just knowing the capacitance alone and not knowing the voltage rating or the manufacturer.
Case in point, circa 1980: I was informed by the Chief Engineer not to use more than one capacitor for any of the sample and hold circuits because the droop rate goes up due to increased leakage with more than one cap. That's one application where leakage is often critical. So perhaps you should argue with him not me
There is also the absorption factor which would also effect droop rate and efficiency, as well as hysteresis.
Luckily, this actual application probably wont suffer too much but i think a test is a good idea anyway.