Also 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.
Go through the guides. Then take your core voltage off Auto and set your memory voltage to factory recommended values. Change the System Memory Multiplier (or whatever your BIOS calls it) from AUTO to 2.00, 2.00B, or 2.00D - whichever you need to set the Memory Frequency to twice the FSB. Then when you increase the FSB, the memory clock will rise in in proportion with it. At an FSB of 200 MHz, your memory clock should be at 400 MHz.
Download CPU-Z to check your FSB:RAM ratio. It should be a 1:1 ratio.
Keep you voltage under 1.45 volts and your reported core temps under 70 C.
The best I was able to get out of my E5200 in a GA-EP35-DS3P motherboard was 3.78 GHz. I was quite a ways from max core voltage and max core temps. The CPU core just would not go faster.