Okay I am wondering if anyone else is haveing this issue.
Presently my q6600 runs stable at 3ghz (48 max temp on full loads) on everything including LinX (1hr) and prime 95 (1hr). I have no issues with any other games or programs but BattleField BC2. Whenever I start BC2 my CPU will downclock to 2.65 GHZ as the game is loading and will stay there until a reboot. I use Nvidia monitoring tools and cpu-z and watch it as it starts to down clock.
It sounds like SpeedStep is dropping the multiplier to 6x when this happens. I'm guessing your FSB is around 400mhz? See if you can disable it from the BIOS. It could be thermal throttling, what kind of temps do you have when this happens?
At 48ºC it cannot be throttling. Thermal throttling only kicks in at 75ºC, so that cannot be it. Also, TT will not reduce the reported clock speed, it actually does things with the power duty cycle, not the bus or core speed. It might dick around with the multiplier, though, but only at 75ºC or above.