It's probably safe to say overclocking a CPU decreases it's life and creates other risks too on your hardware. Likely applies more though to newer higher watt CPU's and such. Your outcome was nice and with your temps your good to go.
Here's an interesting guide to unlocking your Duron.
http://www.ocinside.de/go_e.html?/ht..._painting.html. I have personally never unlocked a CPU but have heard about it. I guess careful comes to mind.