Lifetime is more determined by temperature and voltage than speed. If you keep it under about 1.36 volts and 72C (full load temp), it should be good for a long time (almost definitely over 5 years, even if it is on 24/7)
Cheers m8 .. perfect answer
but 1 more thing .. is it possible to keep the Temp around 72C with Thermaltake TMG iA1 fan ? cuz the water cooling is expensive and im not planning to buy it ..