I have raised the boost clock on my i7-3770 through my motherboard's BIOS, but my 3770 never reaches its maximum boost clock. I have it raised to a turbo boost of 4.3Ghz, but it only goes up to 4.08Ghz under load.
What stress test software are you using? Also what does the voltage get to? You may have to override the Auto Core voltages and manually bump them up your self. If you chose to do this monitor your temperatures because volts = heat.