Hello,
I been using ATI 5870 for the last 3 years now and I'm not up to date with nvidia cards. Anybody have experience with this kind behavior? Is this a driver issue? I don't think its overheating, The card temps are idle(25 avg) and when playing (58F)
 
Prior  to transition to 660ti FTW Sig 2, I uninstall ATI driver, reboot, then shutdown and replace 5870 with 660ti. I installed 310 driver. After playing for almost an hour, I get the black screen then it recover but the FPS goes down to 25 FPS. So I close the game and reboot my system and able to play again but crashes again. So I updated the driver to 314 but no luck, still getting the same issue.
 
Game I play and issue:
Borderland 2 and Far Cry 3 = It takes about an hour before it crash
Crysis 2 = about 30 min then crash
 
My system:
Silver Stone FT02 case
P8P67 pro (3602 firmware) with 2600K clock @ 4.4
Corsair HX850
4 x 2G Hyper X
1st Samsung 830 SSD = Win 7 x64
2nd OCZ SSD steam games