I thought I was rock stable after lots of testing in one case, memtest, prime95, 'stability test' even thrashed the floppy drive. Later i wrote a java applet that hit the cpu cores in both regular and random millisecond patterns - it crashed the machine in seconds. Multicore load effects are something else to look out for then - take a few steps back from the edge and it all matters much less. Its worth it for a solid machine.