Core Temp might be the program you are looking for. It offers trayicons where you can see the temperature, clock speed, an overheat protection which warns you and is able to shutdown Windows or close programs automatically. It also has a Windows sidebar widget, but as far as I know Windows 8 doesn't support the sidebar anymore. I don't know if it has battery statistics as well (I don't have a notebook to test it), but it should cover most of your needs. And it's free!
If you care to analyze your system in a more accurate way, Process Hacker is also able to show you the clock speed with GPU usage, and a few more things. Very similar to Process Explorer. Free as well. But don't forget, the built-in Windows 8 Task-Manager is already able to show you the CPU clock speed.