How healthy is it to OC GPU/CPU?

i just wondering, how much does overclocking destroys the silicon transistors in cpu and gpu, if both was watercooled (120*2)

because if overclocking my cpu makes my cpu life time shorter by half a year, then no, i do not want to, i merely want overclocking for productivity, so....

should i? should i not?

It's mostly heat output, if you can keep both at a safe temperature you won't see much decrease in life expectancy, there is more that just heat, but heat is the major killer in hardware. 

*edit: so yes, free performance > risk (well power consumption but yea)