Just done some more thorough checking - the AGP regulator mosfets are not powered by it....the PLL definately is, VDD and VDDA on the ICS952607 are connected direct to that mosfet output where that 5v mod is) and is definately burning up when at 5v - well beyond its 3.3v rating.
Im not 100% certain about the southbridge, but it was getting hot very quick (more so than normal) when i booted the board with no cpu or ram installed (to test and measure voltages).
Its also possible certain lines to the northbridge are coming from that mosfet output.
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