After a lot of researching I wouldn't go past 55c overclocked myself. With an E6400. This cpu is rated by Intel at 61c on the IHS when not overclocked. The IHS is usually very close (maby a degree or two different) from the cores.
Now I haven't personally tested it, but I have read a forum post where a user tested the temperature of the IHS. The temperatures comming off the IHS and the Cores, both idle and under load. Where almost identical.
So running cores at 70c. Means your running the IHS at 70c. Which is way over the rated limit by intel.
Does this mean anything? I don't know. Lots of people seem content at running at those temperatures. But I am going to play it safe and assume Intel knows what they are doing. And running past this rated limit is going to stunt the cpu's life
If I understand this correctly, you overclocked and got lock ups. So you bring it to the computer store to fix your overclock?
If you don't know how to recover from a bad overclock, I think you should be doing a lot of research before trying again.