some chips overclock better than others, also im no overclocking master, but somethimes u gotta fool around with the right settings to achieve a higher clockspeed on cpu, id ask this in the overclocking section better luck there
The motherboard that you have is not best suited for the desired overclock/CPU frequency that you want to achieve. The maximum, safe overclock on that board would be around 4.2, I would invest in a "better" motherboard.