If you won't OC your chip to its maximum and keep it running 24/7 on high volts and high temps it is probable that it will last a few years
LN2 is liquid nitrogen, a very cold stuff
But this is not exact science you know, it rally depends on all your hardware. Let's say you OC your current CPU, the one one your sig Q9300. It runs at 2.5Ghz stock, 333MHz*7.5. taking it to 3GHz, 400*7.5, with that board and RAM wouldn't be risking that much imo, as the board can handle the OC, and with a FSB/RAM ratio of 1:1 you wouldn't be OCeing your RAM (400*2 for 800MHz). For making it reach the 400FSB, you would need to increasi the voltage a little, say to 1.45V, what would mean that max temps on load would easily reach 80-85ÂºC on low-budget air coolers. If you cool it down on water, with a Corsair H70 for instance, max temps on load would decrease to 60-65ÂºC perhaps, maybe more, and so you wouldn't be damaging your chip so much. however, with 400FSB and 1.45V you will be reducing the chips lifespan significantly, and your board as well. Keeping it cool will help on making it last, but volts will kill it much more fast than temperature. Also, it is likely that your board starts failing sooner than your CPU, or maybe not...
this is all theoretical, as it depends much on the chips too. If i had a Q9300, mine could last longer at 3GHZ than yours, or the other way around... you see?