Best workaround (so far) is to:
Download ThrottleStop and uncheck "BD PROCHOT".
Bad workaround is to:
Change 'Start' value to '4' from the default of '3'. This disables SpeedStep, which means the CPU runs at full speed, and will use more power.
Note that this is for Intel CPU's, an AMD CPU has a similar registry key.
I tried all the other fixes listed here and none worked.
Keywords: Unbearable slow, Processor Throttling, Ghz