I'm not sure that's there's any definitive study which "proves" this, but I can vouch from personal experience that very low/no airflow PCs do tend to break sooner. For more info, just go through some electronics/thermal documentation sites. Try, for example, a search on Tony Kordyban.  What, in your personal opinion (without benefit of specific testing) is a generally safe temperature where these is unlikely to be heat generated degradation of component life... at all. Period.  What do you think about 00C. That is what I use as a target. I didn't get it from any scientific source. I just saw that speedfan is set by default with a 00C redline. Seemed like 00C or less would be safe. As a result, I get uncomfortable when I see temps above 00C. I think that is based on something a little more than superstition, but not much more.  