It's not as though many CPUs will reach the end of their natural lifespan anyway, they just need to last till the next upgrade...
Overclocking a processor could actually lengthen its effective life- once our P75 became too useless to run such gaming monoliths as Mechwarrior 2, we overclocked it to P120 specs. It blew up 3 months later, because back then cooling basically meant blowing on it if you smelled burning, but it still lasted 3 months longer than it would have otherwise, since we'd have binned it.