try and use dx/d2 overclocker. i use it and you can customize voltages to allow you to use the higher speeds more efficiently. jus make sure you test it out before you set it up to automatically boot with it.
You can customize the voltages for the scripts also I just set them the lowest possible for most phones go to sdcard/overclock/the script you want ex. Oc1.4 you will see the mhz after that the vsel that is the voltage raise it till its stable don't go over 90 do this with astro or root explorer.