I confirm the SLI problem (I have two 580 GTX)

It just don't wont to work with the latest 1409 bios . With 1485 is fine.

When using 1409 , with any driver up to 270.X it doesn't give you the option to select SLI in nvidia control panel . Only thing you can select is the physx processor .
If you try with the 275.X drivers and select SLI , the nvidia panel freezes and the 2nd VGA gives a yellow exclamation in device manager .