Your processor may be unlocked, but your board's B75 chipset does not support CPU over clocking. Check this link for details, the second paragraph in particular:
Intel Launches 7-Series Chipsets
You cannot change the CPU multiplier, but you can change the BCLK a little, but not like earlier generation Intel processors. If you're lucky, the BIOS might have a special feature that would allow a non-standard OC (non-Z OC), if that still exists.