Hey sorry ! that after long time i just signed in today,and was unable to help you !
Can u tell me that what options you have got in your bios for overclocking and that way i can help you easily.BTW i didn't done anything special to get reach 2.5GHz, i have just changed my CPU voltages and simply increased the speed from 2.1GHz to 2.5GHz that's it.
i will be waiting for your reply !