Problem Overclocking I5-3570K

Hey there. I have a i5 3570K and a ASUS P8Z77-V LX motherboard and I am really struggling to get it to overclock.

In the EZ BIOS, the CPU will mildly bump from 3.4 to 3.5GHz under performance mode but I cannot get it to shift from 3.4 in advanced mode.

I have noticed the board says the max multiplier is 34 and the default for this cpu is 34 but I thought the K CPUs are supposed to be unlocked?

I have updated the BIOS but whats confusing is I have read other people successfully overclocking with this board.

Do I need to bump the BLCK frequency up?

Apprciate any help.. just come from a FSB Core 2 Duo setup so its all a little alien to me.

Cheers