One of the "geniuses" (editors) at a major PC magazine recently reported "frying" his processor (and a few other things) in an experimental home-built he made for an article. His overclock was fairly mild. Too expensive for me, but his tech support gave him all the parts for the new build.
Forty years ago, when everything was doped junctions, we considered anything over 105C junction temp a "failure" for aerospace/military reliability, and really worked to keep Tjs down to 95C. Junction temps of 105C in the tiny processors of the era would make the case "mildly warm," maybe 30C above room temp. Commercial designers were using about 135C junction limits then. With current "barrier switch" technology, I've seen reports that 305C (junction) is "acceptable," and processor cases do get hot enough to burn you, even with "acceptable cooling." With mild overclocking, you might easily light a cigarette on the processors, if you did it before the circuit paths vaporized.