Your question is vague.
System specs? Drivers?... and FPS - What games and how many?
There is an option in CCC to enable CF for games with no application profile, other than this there is no need to enable CF with the 6990.
You can download MSI AfterBurner and control clocks, fan speed, voltage, etc... also use AB's OSD to monitor the card(s) in-game.
1) Download Driver Fusion HERE
2) Download Catalyst 12.11 beta11 drivers HERE
. but don't install.
3) Download Catalyst 12.11 CAP 2 HERE
4) Custom uninstall all AMD software through Control Panel, select everything and reboot.
5) Run Driver Fusion and clean AMD display drivers - reboot.
6) Re-install CCC and reboot.
7) Install the CAP profile and reboot.