By default, GPU Tweak doesn't come with any program to benchmark or test your overclock's stability. Instead, it gives you the option to choose a program of your choice. What you have to do is go into the Settings menu and point it to the program that you want to use.
3. Then click the TuneSetting tab just right below.
4. Click the ... icon and a new window will open up. Navigate to the location of the program you'd like to use to benchmark or test stability. In my case, I've chosen Unigine Heaven.