I had a similar problem with 8 GB of the same memory you have (although my motherboard is an EP45-DS3R). Gigabyte boards seem to be real picky about memory and Corsair, while a top brand, sometimes has issues I'm told. A few things to look at:
- Make sure your MCH voltage is at auto. Even though I don't want it this way, I've found that any value (no matter how high) other than auto causes something to go wrong (reboots like yours, failing memtest, etc.). With it on Auto the system is stable...go figure.
- I'm not sure about the voltage. With my system overclocked and using 8GB of memory I had to use 2.18V to get it to pass Memtest and keep tight timings. Gigabyte boards have terrible Vdrop and Vdroop which means you have to enter a higher value in the BIOS to compensate. 2.2V should've worked for you...you shouldn't have had to go that high either.
- Set the timings to spec and make sure your BIOS is showing you operating at 1066MHz or lower to start.
-Have you tried each DIMM by itself...i.e. tried to boot with 2GB? This would indicate a possible bad DIMM.
- Go to http://forums.tweaktown.com/f69/welcome-gigabyte-technical-support-24883/ and ask there. There are some knowledgeable folks there.