SB chips are odd things, you can pump more and more volts thrugh them and not gain any stability. I'd work on getting a slightly lower OC stable, then try simply turning up the multi. Every chip has its limits. Regards temps, simple logic. Go play any game or run any real world app thats considered demanding and I bet your temps will top out around 65c. Prime / IBT / whatever are designed to absolutely ravage the CPU, effectively showing instability that will only occur in situations you aren't ever going to run into.