Chip dependent but 4.2 should be doable..... Here's a simple guide though it does boost voltagehttp://www.guru3d.com/articles_pages/core_i7_3770k_and_3750_review_with_z77,13.html
I have Z77, so it's good I guess.
I don't want to set up the voltage so the CPU will live longer...
Any tests or anything about that?