Run it at 48v. If you're stressed about run times, buy another usb battery. The internal AA's will allow you to swap with ease.
4-day long music festivals means lots of batteries and if you can stretch them, it's nice to know what are the exact trade-offs. So, it's nice to know the answers to these questions in order to make informed decisions about buying additional batteries versus running at a lower phantom voltage.
So, following up on some of the responses...the CMC6 body can operate at either 12V or 48V. Does the CMC6 still provide a full 60V polarization voltage if phantom voltage is 12V?
If not, then why would it be a problem if the PFA doesn't provide full polarization voltage at either 12V or 48V phantom?