What is the realistic increase in overall risk running a CPU at modest, but continuous overclock?
Of course I have heard stories involving dead and failed components, frying of this or that, and so on, but the stories seem very few and far between in comparison to total user base, and bad luck appears more often than not to be involved (power surge or unintentional installation mistake, for example).
I also see a lot of people asking about temperatures and HSF/coolers, but I honestly don't see many reports of people having their CPUs completely die unless something exceptional or unusual happens.
One of the most common things I see is that stock HSF are "complete garbage", so I'll ask my more specific question in that context:
I decided to O/C my PII 955BE simply because it was so easy via BIOS, but I'm using the stock HSF.
My computer runs 24/7. CnQ is disabled. Multiplier-only O/C to 3.5GHz. Cores are 40c idle, 55c "real" load, 60c Prime95 load. Computer is under "real" load for a few hours a day.
Although it seems like using stock HSF + O/C is considered near sacrilege around here, should I expect a noticeably shorter lifespan or other tangibly probable deficiencies (as opposed to either upgrading HSF, which is unlikely, or not overclocking at all)?
I guess I'm looking more for justification than peace-of-mind; I am not actually worried about possible failure (whether it happens or not), just curious about it.
The two main factors of your CPU's lifespan are heat and voltage. Generally, the lower these are, the longer it lasts.
As long as your CPU is well within 'specs' at all times (Which is, for that chip, max 1.5v core, max 62c temp. So being <45c idle, <60c load, <1.4v is ideal), you should be good. It's very very rare that OCing will kill the CPU as long as you're careful about it. It should easily last you until your next upgrade.
You have pretty decent cooling performance for stock, but the 955 BE's heatsink/fan assembly is a nice piece of compact copper pipe design. That heatsink/fan would get quite loud though: small fan, high RPM. You seem to be doing okay as is, but if you want to push any farther than a different cooler is definitely recommended.