Resolved! PLLQ maximum frequency reported as 32MHz using STM32CubeMX v6.11.1
Somewhere between CubeMX 6.9 and 6.11 a bug has been introduced that reports the PLLQ can only be less than 33MHz. It is not honouring the Voltage scale set in the RCC parameters.I have set the voltage scale to "Scale 1" but it still reports the PLLQ...