Yea jesse is right on. When i ran 4x512 at home, with 4 performance 512s, it wouldn't run on a 400 bus at all, i had to drop it to 333 and 2T timings to get it to boot. That's with 2x512 HyperX 2 3 2 3200 and 2x512 Patriot XBLK 2 2 2 TCCD. Very few people can get 4x512 to work at 400 and 2T timings. However i've heard of it happening once or twice (outside of 4x512 of tccd...supposedly that works everytime...400 and 2T...1T is still to tight).