I have been running 2 560ti SC for about 6 months now in SLI and they have been great however just tonight i was playing some WOW and out of no where my frames dropped to like 20-30 while flying in the air when just before that i was getting over 160FPS in the same area. So i restarted the game and it did the same thing. Then I updated drivers and it was still having issues. When i looked the MSI afterburner it has the GPU usage on the top card at 99%. It has never been that high before in WOW and the bottom card was at around 20%. I then went into my Nvidia control Panel and disabled SLI and ran both my monitors from my bottom card and everything was normal again. When i used just the top card it went back to lagging and giving me really low frames. I also tested this in MW3 and it gave me the same results. Any ideas on what it could be? Did my top card just die on me?
sounds like the top card is starting to give, have you tried swapping them? is the heat really high on the card? you may want to look in to warranty options. if you can try to test the card in someone elses PC and see if you get the same results.