I have had my i5 3570k since june and have been meaning to upgrade from the stock fan so I could overclock. But the stock fan is fine for the 3570k the CPU does not run that hot that it would need an aftermarket cooler. I can tell you that at room temp it idles around 25-28 degrees and on a load it gets up to around 50-57 degrees at the most and that is with using speed fan. It is by all means not a good heatsink/fan But the CPU has relatively cool temps at stock speed .
The stock cooler is fine. In fact my own i5-3570k is overclocked to 4Ghz at stock volts. Using the stock cooler for now since my liquid cooler pump failed. Will get replacement soon so I can push the overclock