That's an interesting question! technically, intel will warranty a chip if you run it at stock on 1.50 volts if that is its rated spec, because its the over clocking that voids the warranty.
And if thats the case, then it should last over 3 years at 1.50 volts while on stock at the maximum heat in intel spec, 71ish c. So if the TCase is 71c, the cores must be hotter than that.
So then you try to balance the fact that you are using less voltage than that, with the fact that you are using a higher speed, and well under that hot Tcase!
My guess is that you are fine.
Other than my guess, you'll have to place yours, hehe!
I wouldn't mind knowing the way you placed the heat sink on the CPU, and what method you used for applying the paste, too... because it can prolly do better than that.
If you are using the push pins, forget upper question, as they blow, totally. And will ruin your temps!