Sigh. Some good points, some misconceptions, and some wrong things. It's time for some adult leadership.
Shadow's Gigabyte motherboard OC guide:
http://www.tomshardware.co.uk/forum/page-245679_11_0.html
It's for an EP35-DS3L.
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 from AUTO to 2.00. Then when you increase the FSB, the memory clock will rise in in proportion with it. At an FSB of 333 MHz, your memory clock should be at 667 MHz.
You are at 3.6 GHz (400 MHz X 9). That is a 1:1 FSB:RAM ratio (DDR2 RAM, remember?). Any higher and you outrun the capabilities of your RAM. You can generally make DDR2-800 RAM run at -1066 speeds. Increase the RAM voltage to 2.2 volts. Don't worry, that is a safe voltage.
Judging ferom the part number of your RAM, your timings are something like 5-5-5-15. Relax them to 6-6-6-18. That should give you enough headroom to push your FSB higher.
Core2 CPU's are rather insensitive to changes in RAM speed and timing. These changes will have an unnoticable on system performance.
Intel's max recommended voltage for the 45 nm CPU's is not 1.3625 volts. It is 1.45 volts.
http://download.intel.com/design/processor/datashts/320467.pdf page 17.
You can learn all kinds of neat things poking about the technical documentation.
Turn off EIST, work out your OC settings, then reenable EIST. There's no reason to let the CPU run at full speedwhen it is idling.
Compared to the quads, the thermal load of the E-series CPU's are relatively low. You will not need a great cooler to keep your core temps under 70 C.
There has been a lot of discussion about how long to stress test a system. Consensus is that 6 - 8 hours is enough. It just depends how important stability is to you. I stress test for 24 hours. I used to test for 12 hours. Then one day I left a system running over night and idscovered that Prime95 failed at 15 hours. Made changes and the next night it failed at 18 hours. Made more changes, and I let it run 3 days. I then decided that 24 hours is enough.
The P95 small fft's test stresses the CPU. The large fft's and blend tests work the memory harder.
My present systems:
GA-EP45-UD3P | Q9550 OC'd to 3.6 GHz (425 MHz X 8.5) C3 stepping
GA-EP45-UD3L | Q6600 OC'd to 3.6 GHz (400 MHz X 9) G0 stepping
GA-EP35-DS3P | E7500 OC'd to 4.1 GHz (372 MHz X 11)
GA-G41m-ES2L| E6500, OC'd to 3.87 GHz (352 MHz X 11) - limited by motherboard
All are 24 hour Prime95 stable with EIST enabled.