Most mobos automatically disable it when changing cpu multiplier. It may not matter what the options is set to. There are mobos where the turbo multiplier is set differently and you do not want to oc using turbo. You want your oc speed to work no matter how many cores are being used and don't want the mobo trying to figure out voltages for the different turbo steps. If you are set to 45 multi and at 4.5ghz and stress testing, turbo is off already.