Look at your psu manual. make sure you plug the power connectors that have separate 12V rails to the graphics card.
EVGA supernova NEX750B PSU is an average power supply. It is a multi-rail power supply as well so you have to take care in plugging PCIE to gpus so you don;t overload one of the rails.
Thanks for your reply.
So it looks like my PSU has 4 +12v rails, (+12V1, +12V2, +12V3, +12V4). I re connected as follows:
VGA2 (6 pin) from rail +12V2, to the GPU
VGA4 (6+2 pin) from rail + 12V4 to the GPU
I also took CPU1 off rail +12V3 and put it onto +12V1 with the 24 pin ATX for the MB, which meant that all SATA and PERP cables ran from rail +12V3 to the various fans and drives.
This is about as spread out as I could think to distribute connections between the rails.
When I ran 3d mark again, I was able to get through all 3 tests without a crash, however, I still got a lot of coil whine from the PSU or GPU (still convinced its the PSU), when running ICE STORM and CLOUD GATE, and a small amount when running FIRE STRIKE.
Is there anything else I could be doing to remove coil whine all together, or is this indicative of a faulty PSU, or even the wrong PSU?
As a further question/thought, is the coil whine related to the crashing issues I was experiencing? Or are these two separate issues that happened to hit me at the same time?
EDIT: I also switched vertical refresh to always be on in CC, not sure if this has an impact?