That all depends on your chip, and how well the HSF is seated. Some folks say don't OC at all on your stock cooler, but there's nothing magical about an aftermarket HSF. You can probably make 3.7-3.8, or maybe even 4.0 with a golden chip, if you can keep the voltage low enough. I haven't actually touched a 3570k, but I have plenty of experience with the 2500k. A good 2500k could hit 4.0 on the stock HSF, no problem, and still keep safe temps. The 3570k runs hotter, I hear.
But in any event, you'll need to make sure that the fan on the HSF is set so that it will spin up as fast as it will go when things start to heat up, so to keep the chip safe you're going to have a leaf blower on your hands.