There is NO clear Yes or No answer to predict "life expectancy" regarding to a particular CPU based on voltage and temperature. For a given CPU type, they follow certain statistical behavior.
The inverse relationship between frequency and temperature will naturally determine the max voltage and frequency for a given CPU and cooling setup. If overclocking is done properly, such voltage and temperature should be below the max absolute temperature and voltage of a given CPU specifcation (at least true for Tbred/Barton).
For example, assuming nominal voltage is 1.5 V.
Running it constantly at 1.8 V is 20% over nominal and running it at 1.95 V is 30% over nominal voltage.
From electromigration analysis, keeping temperature roughly constant (by cooling), overvoltage from 20% to 30% decreases CPU failure time (life expectancy) by about 10% (failure time reduced from 69% to 59%)
For Tbred B/Barton/Mobile Barton, the frequency gain between 1.8 V to 1.95 V is about 75-100 MHz at 2300-2500 MHz level, it is stating to operate in the diminishing return regime, getting only 75-100 MHz from 150 mV Vcore increase. The gain in overclocking frequency is about 3 - 4%.
The most effective, cost effective overclocking voltage for Tbred/Barton is between 1.5 - 1.9 V, beyond which overclocking is very costly in terms of power supply and cooling with diminishing frequency gain.
So it is a tradefoff between frequency, voltage and life expectancy.
Going from 1.8 V to 1.95 V, one would get 3 - 4% increase in overclocking frequency at the expense of an additional 10% reduction in CPU life expectancy (statisitically).
But then a different person uses a CPU differently and have different objective, some expect to use it for 6 months, 1 year, some for 3 year, ..., some want to squeeze the last MHz for competition and satifaction, so one has to make his/her own judgement and tradeoff, ...
This post discusses this subject in details:
CPU voltage: from stock to max absolute, from efficient overclocking to diminishing return (page 19)