The common wisdom is, the hotter it runs, the shorter the CPU life. Generally, the more you overclock a chip, the higer the voltage needs to be for it to be stable. The higher the voltage, the more wattage, and heat, the chip sees. The other side of the coin is, the hotter the chip, the less stable it is. This means, if you use a 650 instead of an 800, you may have to up the voltage, and spend the difference in the price of the chips on a better cooling fan. Nobody can tell you how long it will last, but cooler is better and every chip is different.