AMD Phenom II x2 550 BE
4GB Patriot Viper II DDR2 8500 1066
Vista 64 bit
XFX Radeon 4870
Antec BP550 PSU
I ran Prime95 and got an error after just one pass:
FATAL ERROR: Rounding was 0.5, expected less than 0.4
Hardware failure detected, consult stress.txt file.
The only thing I have done was change memory voltage from default of 1.8 to 2.1 to accomodate my memory specs and get 1066 to read in the bios. By default the bios read memory at 800 because of default voltage of 1.8.
When I changed the voltage back to 1.8 and ran Prime95 it passed.
Patriot Viper memory is sketchy. I had a set of Viper DDR2-1150 ram rated for 2.3V. It would not pass memtest at 2.3V. However, after lowering it to 2.0V, I could get it to pass. But it still wasn't fully stable in my computer, so I ditched it. So, from my experience higher voltage for that ram could make it run worse. If you try it at different voltages and can't get it to run at 1066mhz, then get an RMA.
I had more issues last night while gaming. I underclocked the memory back to 800 and ran Prime95 overnight. No errors. Not going to RMA it. I have nothing to use while I wait a week or 2 for new memory to show up. Shame on me for buying Patriot Memory.