The easy answer is that if your computer doesn't function correctly than it's not stable, no matter how many hours of stress testing you've done. You can up the voltage (those things will take up to 1.5V on the core without issues, but don't go higher) or if you're already near the voltage ceiling you'll have to back off the clock. In your case you might be able to make it stable by increasing the VTT (FSB voltage) to 1.30 or so, and make your MCH (northbridge voltage) around the same as the VTT. You are close to stable if your chip is taking such a beating, just some minor tweaks will fix it.
Good luck!