I have always used (before using the 12 channel MPX RX) unregulated 5 cell packs with 22 gage wire in Isobars (roughly the size of KingCat). I figure that the voltage drop over the wire runs helps to compensate for the lack of any voltage regulation. I have never had any issues what so ever due to not having a regulated 5 cell pack. Loose the regulators, just another possible failure point.

P.S. the isolation circuit in the 12 channel receiver is a diode scheme that cuts the voltage down a bit, therefore you have to use a 5 cell pack. No need to regulate.