I am building a new a new computer and plan on doing some mild overclocking. Nothing extreme. I have an AMD phenom x2 560 on an Asus ASUS M4A88T-V EVO/USB3 board. Is the stock heatsink any good? I have not unlocked the other 2 cores yet. I cant seem to find much info on the stock cooler. Thanks.
Your system will run warm with the stock cooler, but should be adequate for a mild overclock of around 10 percent or so. Main reason for the 10 percent guess is most chips/motherboards can achieve a 10 percent overclock with out raising voltages. Once you start raising frequency and voltage, stock heatsinks usually start having problems coping.
Of note here is that not all AMD Phenom OEM HSFs are created equally. Some are nothing more than bladed blocks of aluminum and others actually have copper heatpipes. If you have one of the higher end (with copper heat pipes) versions, you should be fine as long as you don't go OC crazy. If you have the more basic version, I wouldn't recommend OCing with it at all.
...and they are noisy as hell when the fan is going flat-out to get your CPU temps down to a reasonable level. So get used to the noise or get an aftermarket cooler that uses larger fans that run at lower RPMs.