I just got this memory in the mail today, and right now I am doing DDR500 (250HTT) w/ 3-3-2-5-1T timings @ 2.8v. Have not found the limit yet. This memory was recommended to me at XtremeSystems.org. This memory reached 270HTT 1:1 at XS with the same settings I am using: http://xtremesystems.org/forums/showthread.php?t=77205