it's not just heat people. electro migration. thats a bad thing. it's an unstoppable phenomenon that happens with all micro electronics. it happens slowly with non-overclocked cpu's, but it is accelrated by overclocking. Both heat and high-voltage are factors.
A link to [H.
So even if u got good temps, don't go crazy on the voltages. Over 1.80 is going into more "risky" teritory, but overclocking is all about risk.