I am almost certain 0123 supports Quad core because the P5K deluxe supported quad core on release and 0123 was the release BIOS.
I was experiencing the excat same problem as you but solved it by doing as I said.
Here was my post in this thread a long while ago:
http://forums.hexus.net/showthread.p...87#post1135487
And here are 2 other threads that helped me get around the problem aswell:
http://www.hardforum.com/showthread....1629&t=1200834 http://www.xtremesystems.org/forums/...d.php?t=147927
I bet your system will work perfect in all of the latest BIOSes when running just 1 stick of ram as that happened with me aswell, but as soon as i put the 2nd stick in i would get problems. But both sticks were 15hours memtest perfect!