Another issue on the non kingpin bios is the SRC Power limit linked to the 8 pin rail.
While all of the 8 pins have a "global" power limit, which is only one value which is related to TDP (8 pin + PCIE Slot power limit= TDP),
Each 8 pin has a "SRC" rail linked to it, which is usually 150W default, 175W max, and this limits the max 8 pin power draw (the 8 pin power limit doesn't, the SRC power limit for that rail does).
So there are 3 SRC's for three 8 pin cards.