Ed,

Yes, I am for equal load sharing. That is ideal. The trick is to make sure both regulators output identical voltages all the time (or within 0.005v as you mentioned). Otherwise, one pack will get used more. In the extreme case that the battery is deeply-over-discharged (lower than 3.2v/cell for TP), it could become useless. Even though the plane is saved because of the backup, the main pack is ruined.

This is the worse scenario for equal sharing mode. I was hoping that the regulator will not allow the pack to drop below 3.2 before let the other to kick in. But the capacity of each pack in equal sharing should be the same and its capacity sized as if there was only one pack in the system, if the condition that equal voltage from the regulators is not guaranteed all the time.

For hot-standing, the backup pack can be of a lower capacity (minimal of one flight), assuming the voltage of the main pack is checked before each flight.