Nothing man, it's very simple, you've already seen how it goes. You know the theory and apply it correctly. You keep increasing the frequency, you keep passing stress tests until it's not stable, that's the limit. If you increase the voltage minimally you can check if it goes up a little more, but it's very likely that temperatures will increase, and you may not achieve stability, that's normal.
In total, as long as it doesn't reach 70º degrees or pass it, it's fine. At that temperature under full load it has reached as far as it can go. It's so random that even 3 micros identical to yours can reach values with up to 1/4 of a difference between them, both in frequencies and temperatures. So you know, it's not an exact science in any of its aspects
Best regards!
Well many thanks Sylver, maybe next year I'll dare to raise it to 4.2 Ghz, but I don't know if it will be worth much the truth. From 4.0 to 4.2 Ghz I don't think the gain will be much, I speak from ignorance of course.
Best regards!