I have...
1) Tried each card individually to verify they work properly on their own.
2) Tried each card in SLI in either slot (card 1 on top and card 2 on bottom, vs. card 2 on top and card 1 on bottom).
3) Pulled the BIOS file from each card and compared the CRC32 checksum to ensure they have identical BIOSes.
4) Done a full uninstall of afterburner and the drivers themselves, (even though it would make no sense, just because...), then reinstalled the drivers clean and left afterburner uninstalled, used two copies of GPU-Z to monitor (1 per card) and then run full-screen games...
...and the behavior remains identical through 2, 3, and 4. On their own each card works properly and will go to 1.243-1.250v on the core, but in SLI they power target limit at 100% even though the target is set to 110% and the card read as GPU1 without fail is always 0.05v less on the vGPU regardless of settings.
Finally, I have tried both drivers 344.11 WHQL and 344.16 WHQL and the behavior persists.