i think this is indicating a ram problem for you.
i have ocz platinum rev 2 and an opteron 165.
its running at 2.7ghz stable, but my ram wont go very much higher and still be able to pass prime. i can run it day in and day out as long as ram isnt too high. i am getting the exact same errors as you are.
use a ram divider and set it down.
although i can run stable at 240mhz ram speed, i cant pass prime. so thats why i leave it at 200mhz.
FATAL ERROR: Rounding was 0.5, expected less than 0.4
Hardware failure detected, consult stress.txt file.
[Sun Mar 12 18:02:35 2006]
FATAL ERROR: Rounding was 0.4997086606, expected less than 0.4
Hardware failure detected, consult stress.txt file.