If you are running at 1:1, your memory clock (BIOS) at stock should be 533 MHz selected by using a System Memory Multiplier of 2.0. So at 3.0 GHz (333X9), your memclock should be 667 MHz.
For a review:
HOWTO: Overclock C2Q (Quads) and C2D (Duals) - Guide v1.6.1http://www.tomshardware.com/forum/240001-29-howto-overclock-quads-duals-guide
Shadow's Gigabyte motherboard OC guide:http://www.tomshardware.co.uk/forum/page-245679_11_0.html
It's for an EP35-DS3L but all the Gigabyte Core2 BIOS's are similar.