im using a fortron 350W (400W) psu, so dont be surprised by the dipping 12v rail wth both cards under load ^^
this is an old psu with low watt rating, but its a quality psu, fortron btp series.

psu rails:
12v 12.10 idle 12.00 load
5v 5.22 idle 5.23 load
3.3v 3.38 idle 3.38 load

rails meassured on the mainboard:
12v 12.10 idle 11.96 load
5v 5.22 idle 5.23 load
3.3v 3.38 idle 3.38 load

rails measured on the pciE slot: (2nd from right when having the mainboard layflat and looking at the back of the vidcard. this and the following pins are 12v, then a couple of ground rails and then the 3.3v rail)
12v 12.06 idle 11.93 load
3.3v 3.36 idle 3.36 load

videocard volts (massured on the cap legs on the back of the card, 2 caps close to the videocard fan plug are vgpu, the other cap on the edge of the card is vmem)
vgpu 1.43 idle 1.45 load
vmem 2.10 idle 2.12 load

11.93 sounds low, the board is eating .4v from the 12v rail...
i will bump the 12v rail and see if it helps to get a higher oc... but i doubt it