Anything that goes towards 70 degrees celsius will be a concern. If your cpu is running too hot, you might consider buying a new cpu cooler.
Try a Hyper 212 EVO to cool!
If all you want is a two year lifespan, even 80C would likely still be perfectly fine. Below 70C, it will likely last until something else blows up.
if-2500k max core temp before throttling occurs is around 95C. Personnaly Mid 60's is fine, I try to stay under 60 when say gaming. For short duration suck as runing prime 95, I do NOT like above 75 even though 80 is acceptable.