I don't think OCing without messing with other things, like voltage, will have a significant effect on your CPU's lifetime. Still, a 2500K at 4.0ghz should have no problem handling that card in any game but Skyrim (maybe bump to 4.3ghz there).
If your ambient temps aren't crazy and your case isn't stuffed into a box, you shouldn't really be seeing temps like that. Test again with PLL OV off. How did your TC application compare to this technique? http://benchmarkreviews.com/index.php?option=com_content&task=view&id=170&Itemid=38&limit=1&limitstart=5
65C is totally safe, but I'd expect more like 58C.