I'm pretty sure you can OC it with the stock cooler to just about 3ghz. Make sure you keep an eye on your temps though. Why not just get an inexpensive aftermarket cooler like the coolermaster hyper 212+? For around $30 you can get an excellant cooler that can OC the processor 3.5+.
When I bought my CPU & mobo at Fry's I was seriously considering buying that exact cooler.
If I decide to OC, I'll probably pick one up.