Oh... how do you change that via CCC?
or can you not?
Catayst Control Center is the worst tool for overclocking, but it's also the safest. The best one to use is MSI Afterburner. It gives you fine grained control over the core clock, memory clock, core voltage, memory voltage, temperature based fan control (which is awesome), detailed monitoring, etc... You will have to unlock the voltage control from the settings menu but be warned, increasing the voltage will cause the peak temperature to rise FAST so be careful.