You will get different answers from different people, but I use 2 hours of prime 95 blend to get an idea of general stability. I also make it a point to surf the web and even control-alt-delete occasionally to throw it a curve while it's under load. (This has actually caused BSOD's in overclocks that were holding it together under prime up to that point)
For temps, Intel burn test at very high or maximum seems to really push the thermal limits of your CPU/cooling.
Then I throw in some video benchmarks like 3DMark11 and Haven DX11.
And finally I go through a couple levels on a video game.
If it makes it through all that, with no hiccups or heat issues, it's good to go in my book.