As people have said, you cannot get it lower than room temperature.
I do have to disagree about the delidding risks, however. Yes, it voids your warranty, but the vice method is incredibly easy. I've delidded two 4770k processors with no problems. First try was a success with no prior experience. Second time was even easier.
And it's not that small of a gain. I dropped 20c at load on both CPUs. I am running 4.6GHz @ 1.22v or so, never goes above 60c at full load with merely a Corsair H60. My idles have dipped to 16c minimum when my room is that cold.