I want a high level of performence but also a system that will last years and not overstress the components.
I wouldn't worry about it. I know of a Socket A (Barton 2500+ mobile) that was only retired last year, running 24/7 with a 30-something % overclock the whole time (on air), a socket 939 rig (opty 146) which was retired 2 weeks ago with a 25ish% overclock, again 24/7, a socket 478 (p4 northwood) that's got a 25% o/c which is still running....
As *most* people will upgrade their rigs well within every five years (yeah, ignore the guys I mentioned above!), saying that overclocking reduces the lifespan of your chip is not necessarily true. If you buy a chip and plan to upgrade within 5 years, then that chip's lifespan is 5 years, not the 25 or so that the manufacturer expects (who is really going to be running a chip 25 years down the line?!).
Obviously there are exceptions to this, especially when it comes to overvolting and overheating, but if you keep everything within the safe levels, you'll throw away/sell a perfectly good, albeit dated chip when you move on to your next rig.
Saying that though... almost all cpus these days have more grunt than the majority of people know what to do with!
