Honestly it varies chip to chip. I could tell you that I can get a 3.2 Ghz overclock, but your chip might only handle 2.9 Ghz.
The best approach here is to just step up the clock, stress test, and repeat until you reach instability, then dial it back to the last stable clock and that is your overclock. You can play with the voltage a little bit to try and get a little more out of it, but that carries a lot more risk.
Your other approach is to use Google and see what other people in other forums have been able to overclock the chip to and try to match those settings, but your hardware might not perform the same as theirs.