this error always occur due to bad response time of gpu....
hope you can understand ...http://www.tomshardware.com/answers/id-1755834/nvidia-display-driver-stopped-responding-recovered-error.html
you can easily push it at 4ghz with this cpu cooler... increase the multiplier ratio and best tip for tha cpu is that slightly decrease NB frequency and raise vcore by 0.0025+ and so on ...