I like cpuburn as a stability tester. In my experience it is very good at loading the CPU. It is good, however, to test using multiple programs (not necessarily at the same time). When I'm going for absolute stability of the mem and cpu (ignoring graphics), I usually run 24+ hours of memtest86 (running all tests), 48+ hours of cpuburn, and 5 days or so of prime95. It may border on the obsessive, but I like to be that confident in my system, otherwise if I get the slighest software problem I have to unoverclock, recompile, and run the program again just to ake sure that my OC isn't causing problems.