No need to un-install CCC. Can't remember if setting it in ATI Overdrive stopped the GPU from going back to 500 MHz on idle. Could try that first and watch the current clock settings and make sure it stays at the higher value you set it at when at the desktop.
I have posted a screenshot for the menu options for overclocking in ATI tray tools, just set the values at the normal clock settings for your card.
Make sure you tick 'Include clocks in Profile' and 'Load selected profile at startup' if you want to keep the settings for each program startup. Then hit the save button at the bottom to save a profile.
The two screenshots values are just for reference. Set them to your normal graphics card clocks.