Quick update on the regs... apparently there was a little glitch in one of the 4 that I have. It works fine solo, but for some reason is not sharing power in a balanced reg set-up. Even so, that particular regulator was still working fine when the other was completely turned off, so there never was any danger of the Rx losing power. If anything, a good illustration of the dual redundancy idea in action.

Installed the 2 new regs today and both are tracking voltage drops in the Lipos to an extremely tight tolerance, always +/- 0.01V.