every one has a different opinion on it but i dont run prime 95 as it puts your cpu under stress it not going to see in real life use
to me my overclock is stable if it doesnt crash when doing the stuff i normally do like heavy gaming and video encoding etc
those temps dont look seriously bad--you could change your heatsink if it bothers you
There's something to what your saying, but it's not the full picture. You can be slightly unstable depending on what your running and not crash. Now that's great if you don't crash, but you will over time corrupt data on the drives. If your one one of those people that format often, then it's not a problem. If you don't, then making sure the system is fully stable is important. Just my 2 cents.