What happens when you lower the overclock? It may have something to do with the fact that a stress test is a solid 100% load and doesn't vary , where BF3 is a game with ups and downs in the rendering of the game so it can go from low stress to high stress in a flash and the fact that you may be at the limit of what you can overclock the two 560Ti's , that gameplay action is what may be too much so try lowering the OC a bit and see what that does.
I don't know if the voltages are unlocked. I just use EVGA Precision X. The cards come factory overclocked at 900/2106. When I OC to 950/2190, it runs pretty much anything stably. 990/2190 I just get a black screen after a few minutes. I have done all this at 1.075 volts.
That's unusual to have damaged the OS , what exactly did you damage and why don't you put in the Windows disc and do a repair of the OS. Internet Explorer is a part of the OS as it's an application that connects to the internet and by saying that you damaged the OS this could have an affect on the way IE works. Games use programs like IE , firefox and google chrome to play the games on the internet.
I'm not sure that you can damage the OS by overlocking so can you give some info on what happened and why you think that the OS is damaged.
Well, before I attempted for 4.8, I could run 4.5 at 1.28 volts stable. After going for 4.8, and crashing during boot on windows, I could not get 4.5 at 1.28 volts stable. I just BSOD a few seconds after boot.