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.
MAGNETIC SLIP
What are the sealing arrangements of the HP pumps? Do they have a double
mechanical seal or are they
magnetically coupled?
If they are magnetically coupled (mag drive) then they can suffer from
magnetic slip and lose coupling all together. This would not necessarily however show signs of cavitatation. Magnetic slip can occur quite readily in large pumps when the demand on them is too sudden (on electrically driven ones, the star-delta needs to be set up to apply demand more gradually).
FOAMING
Does anybody know anything about the foaming tendencies of Jet A1, especially at low pressures and temperatures?