See what the AMD Overdrive utilty will do. Keep you settings auto in the BIOS then let the util work for a few hours, including reboots. It will adjust multiplier and voltage, so if you pay attention you can get an idea for some manual settings and due stability testing on your own. Also it has a "quick settings" which can be VERY aggressive, so start at 0. You may have to set to 1, apply, the back to 0, apply, something the first setting doesn't stick.
As for disabling cores, this is more manual and probably not as practical since it requires switch them on and off manually, but you will get better overclocks (technically).