I was working with a Lenovo user today who has a 2920XM and the turbo TDP/TDC limits are locked in the bios and can't be adjusted using ThrottleStop. He didn't have any success with the ThrottleStop Turbo Ratio Limits either. He has an unlocked CPU but if a laptop manufacturer decides that they don't want you pushing your Extreme CPU to its limit, it is simple for them to turn off its capabilities in the bios by setting a single bit in the CPU. We can only hope that Alienware isn't going to be this anal or someone is going to have to learn how to modify a bios or two to correct this problem.
As for traditional BCLK overclocking, Sandy Bridge is known to be limited to between 0% and 5% before losing stability.