So far tried the following:
7970, Slot 1, bios 1.5, dE post code, no boot, no lights on GPU
7970, Slot 3, bios 1.5, dE post code, no boot, no lights on GPU
7970, Slot 5, bios 1.5, dE post code, no boot, no lights on GPU
8500GT, slot 1, bios 1.5, dE post code, no boot, fan spins, no other life signs
8500GT, slot 3, bios 1.5, boots perfectly
8500GT, slot 5, bios 1.5, boots perfectly
Seemingly 'dE' points to a DXE error which I've been told suggests an internal error on the board.
Just rebuilding back into the UD7 now to test the GPU. I can imagine a package containing a board AND GPU costing me a fair chunk to post to holland, I know I can send them back to respective retailers but I'd rather deal with everything through one person, in this case its all MSI.