http://forums.nvidia.com/index.php?showtopic=192020
There are issues with the current drivers for the 560, and Nvidia has failed to awknowledge the problem even though it is all over their forums. Not saying they don't care, but from what I can tell based on most people's issues, it appears the current 560 drivers cannot support OC'd cards, but they have not cornfirmed/denied that there is an issue.
I had 2 560's in sli and the same issue happened to me. I had the gigabyte 900Mhz core cards, and the first time I run into an enemy and fire in crysis, screen goes black, and sound loops in the background until I hard reboot the computer. Rift also could not withstand any Rift event. BFBC2 would have the same issue within 15 minutes of playing any map. I got sick of it, and couldn't find any answers, so I took them back and got 2x 6950's and flashed them to 6970's, and I couldn't be any happier. But it is all up to you, as COLGeek said, I just thought i'd let you know about the current nvidia driver issue with the card you specified...Although I have posted that a few times on this board, and everyone seems to ignore it....Either I am an extreme minority with having issues (had it on 2 seperate cards, in sli, and each of the 2 cards individually), or no one else has owned a 560 to test the problem.
Edit: This only applies if you are OC'ing the card, or get a factory OC'd card, reference models seem fine.