It has many factors in determining that. You wont hurt your cpu if you just stop when it becomes unstable. Abit is genrally stable but it depends on your mobo, RAM, and cpu core, stepping revision. To find out the cpu information, download cpu-z. To test to see if stable download Prime95.
What is your ratio of RAM to CPU?
What are the stock voltages?
What are your ram timings?
You can raise voltages up atick. Here this will help you http://www.ocforums.com/showthread.php?t=263753
But bassiclly, if you stop when temps get too high and unstable thats fine. It is when people keep going regardless if stable or high temps.