i5 3570k what is a good stable overclock?

I am shooting for stability on my 3570k. I am currently at 4.5ghz. I had my graphics driver shutdown on me and some peculiar things happen at 4.6ghz. It's been awhile since I built a new computer. I just want stability. I have seen overclocks of 5ghz. Is there a mean of what people are running at? 4.5ghz is very stable for me at 1.3v in the bios. What is the standard stable overclock on air? These chips pretty much seem the same. Nobody posts what they run at regularly. Also what are the maximum temps that are safe for this chip? On burn in tests I hit 70C, that was the max on one core after a few hours. What is the wall the 3570k hits before the voltage needs to be cranked up?