If your temperatures drop, it means that you have inadequate airflow through your case.
BTW, your sig indicates that your memory overclock is drastically limiting your CPU overclock. You should be able to reach at least 3.3 GHz with even a medium quality CPU cooler.
Check this out.
HOWTO: Overclock C2Q (Quads) and C2D (Duals) - Guide v1.6.1http://www.tomshardware.com/forum/240001-29-howto-overclock-quads-duals-guide
Next stop should be a guide for your particular motherboard. Google is your friend.