the reason I use prime95 is because my system can passed memtest with 1600MHz, it just can't passed prime95. At 1333MHz 8-8-8-24 1T @ 1.8v, it passed memtest and I also ran prime95 on it for 8 hours without errors so that's why I use prime95 instead.
I am running 3 cores right now. I have no problems running memtest at all with 1600MHz 8-8-8-24 2T @ 1.9v. It just wouldn't passed prime95 and there are a lot of bios lockup when trying to configure bios or lockup during dos mode.