I have the 560ti SLI setup and have been troubleshooting for the past 48 hours trying to get BF3 not to fail.
After all my research and tweaking, i've found that the problems your experiencing have NOTHING TO DO WITH YOUR HARDWARE.
THe beta nvidia drivers are crap... and the beta frostbite2 engine is way buggy.
The solution for now is to drop your overclocks (if you have them) back to reference on the cards.
Do a FULL driver wipe for nvidia drivers. Reinstall the new beta drivers from nvidia.
Lower the settings from Ultra to High on all settings in the game. Leave AA at 2x.
You will not experience any crashing after this. You will however still experience serious artifacting in certain points of the game.
I figure as long as you know its not your hardware, theres not much to worry about