This is wrong on Phenom II(or it is on my Phenom II 940 BE and Dfi 790FXB)
I can run max 24/7 3.7ghz in Win Xp sp3 32bits and runing same in W7 64bits without any troubles in game etc.
And also 3DMark2006 do not lose over 0-100mhz from runing in WinXp vs W7.
Maybe you cpu is bad or something, or doing something else wrong?

, but mine dont lose anything in W7 64bit
And all this is with same settings in bios.
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