Hey hujack.
I highly recommend that you talk with nagasama about overclocking. Especially since you have an AMD processor. He's an expert at AMD overclocking.
Since you have a stock heatsink, you won't go very far. I'd suggest you get an aftermarket heatsink, such as the Arctic Cooling Freezer 64 Pro. It's only $20 at newegg.com.
Overclocking does reduce the CPU lifespan, but it's so little, it's nothing to be concerned about. The average lifespan of a CPU is about 10 years. Overclocking will take off 1-2 years, depending on how much you overclock. And I assume, you won't be using that CPU, for 8-9 years.