Yes disable the speedstep and from what I have read, alot of people disable a bunch stuff like Execute Bit, C1E something, Spread Spectrum. there's about 6 or 7 things to disable but definitely the speedstep, some say it causes instability issues.
I myself will be trying the undervolting overclock tonight. 3.9Ghz @ 0.9v. Have you looked into that idea?