Have you got both cards in orange slots?

You could try a single TITAN in the top black slot.

At that resolution you should be getting around 120FPS. with 4xAA.

I started to have a look through that NVIDIA thread earlier and did notice some similar issues. I'll have another read through in the morning.

I'm sure you can use GeForce 314.22 WHQL on TITANs, you may want to try those. Of course doing a full removal of 331.40 and clean in safe mode.

EDIT: BTW What is the clock speed of the GPU doing when the fps drops? Have you tried prefer maximum performance in the NVIDIA Control Panel.