phil - you asked about the speed of the HP fuel pumps and how they are controlled - it should be noted that the pumps are not electrical driven but are connected to the the gearbox and as such the gearbox is driven via a shaft which is in turn connected to the N2/N3 compressor spool so the pump speed is not and can not be directly controlled.
regarding the theories about a missing phase from the IDG, this would be sensed and the idg would be disconnected immediatly so that is a non starter