560ti SLI clocks all over the place (not performance on demand)

My 560ti SLI rig has been acting very strange (well a little strange from day 1, but getting worse).

I've had to back off the memory clocks excessively to prevent artifacting in quite a few games (Skyrim for example)

Upon doing some testing with Furmark, I've found a new huge problem, if I don't detune the cards to say, 750/1500 (from 850/2052), one or sometimes both cards will continually change, going anywhere from proper clock (850mhz) down to 425mhz. In the Nvidia control panel the global policy for power management is 'prefer maximum performance', and I've applied it on furmark's profile aswell.

Things tested:
- Disable SLI (either card works fine on it's own)
- PSU voltages. (Hwinfo64 reports my 12v rail never drops below 11.976v, so it doesn't appear to be a power issue)
- Thermal throttling. (Card temps never get past 80c, so it isn't a thermal management issue)
- MB bios (running the latest version from Gigabyte)

Is it possible that it's a problem with the SLI bridge?

Rig details:
- i5 2500k @ 3.5ghz
- CORSAIR Enthusiast Series TX850 V2 850W (single rail psu)
- G.SKILL Ripjaws X (4 x 4GB) DDR3 1600
- 2x EVGA 01G-P3-1561-AR (whoops forgot to include this at first

Any help or direction would be very appreciated!
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More about 560ti clocks place performance demand
  1. Could possibly be a firmware issue. Make sure that your motherboard has the latest firmware installed
  2. Already running the latest firware.

    New test, with bizzare results.

    Turning up the core voltage to 1050mV (one card defaults to 1000mV, the other to 1012mV) made the clock cycling even worse... conversely? Dropping to 950mV (the lowest msi afterburner lets me go with these cards) nearly eliminated the problem. I'm very, very confused now.

    If it's not a thermal issue (gpu temps attest to that, and the fact the issue is present within moments of starting furmark and doesn't get worse with time confirms it), and it's not a psu issue (12v line still seems stable)... bad vrm's on the cards?

    Like I said, very confused.
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