It depends which power saving feature you are talking about. For example, EIST doesn't do any harm to your OC settings because it does not reduce voltages. What it does is reducing the clock speed by changing to a lower multiplier during low consumption. When you run Orthos or other stress test programs, it will automatically bring your clock speed back to maximum and you will still enjoy stability because (again) voltages are not reduced

I think this would help:
http://forums.tweaktown.com/f69/power-savi...-scaling-31664/