This should be your first stop.
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 motherboard but all the Core2 Gigabyte motherboards use a similar BIOS.
Drop the System Memory Multiplier to 2.0 if you can.
You should be able to reach 3.0 GHz easily. You will not be able to go much higher. Your upper limit will be around 3.2 Ghz because of your motherboard.
At 1.275 volts, you have a lot of room to increase your core voltage.