Finally, Asus fix the stability issues with Corsair 6400C4! There is no need to do manual adjustment now, enabling the SLI DDR options works just fine regardless of optimal or high performance setting. There is no more black sreen whatsoever no matter how many times you reboot. Also when you set the memory to 4-4-4-12 1T, it passed gloriously all the memtest. I will update more on the overclocking performance.
PS: By the way, for people who do not see any difference with the new BIOS, probably after flashing your bios, you need to clear the CMOS first, then boot your computer again.
Also I do not have any other RAM (such as OCZ) to test, so I cant really comment on their stability.