According to TechReport, the free overdrive is over

Although full overclocking only works on Intel's "K" processors, Turbo Boost allows some leeway on models with multiplier locks.

All in all, with such processors, the Turbo Boost multipliers can be raised four times higher than the original setting, giving you virtually 400 MHz - for free. According to TechReport's analyzes, this is now over, and this solution does not work with fourth-generation Core processors (Haswell).