That's the whole point. You want the overkill stability test.
You can run a system that fails prime after 11 hours and say it was stable for 11 hours, good enough. It'll boot OK and seem to run everything OK but the big picture is most people don't feel comfortable running an unstable system even though it's 'just a little unstable'
Remember the Pentium fiasco? Even though the Pentium 'errata' (they called them) were such that most people would never use the kind of calculations that were flawed in that Pentium chip, the mere feeling they were working with an unstable or flawed chip was enough to put them off in a major way.
I'm going to have to bump up the voltage, prime failed after several hours . I think I'll be able to stabilize it at 2.5 ghz however. I'm running higher ambient temperatures than usual since the ac blower died recently.