OK I have some further information which hopefully will explain things a little more.
The 990FXA-UD5 will have Vcore drop from 1.344V to 1.296V under loading even when Core Performance Boost and Power Saving options are off. (absic note - I would guess this applies to all of the 9 series boards but it is only a guess)
Earlier 7 and 8 series motherboards don't suffer from this because the motherboard hardware on these does not have load line calibration design.
The 9 series motherboards do and follow AMD's AM3+ design guide line for LLC.
I also had a chat with AMD in the UK today and they confirmed that this board is operating within their specified voltage range and how they would expect it to. They also told me that they do not recommend Overclocking, so ..... nothing new there!
They also stated that If you disable the Turbo Core Feature the CPU Voltage will drop to around 1.30V. This is because, unlike using Turbo Core you are attempting to run all of the cores at a stated value whereas, for example on the X6 processors, Turbo Core actually disables 3 of the cores and only uses the remaining ones for the speed gain. Lowering the voltage across the processor when all the cores are enabled, is done by design to help protect the CPU and is not a fault.