I have to assume (since you haven't stated) that you have good case ventilation. A CPU cooler is only as good as the temp of the air it is cycling through the Heatsink. Less than optimal case cooling will always result in less than optimal CPU temps. My experiences are based on strong case ventilation, as it was something I learned from customising my cars when I was younger: Cooling first, Horsepower second.
Stock HSF with AMD chips generally only allows mild overclocing before heat becomes an issue. I was able to OC my 710 to a daily 3.25ghz (from 2.6) with the stock cooler. This was more than mild, but I was really pushing the limits of the HSF, running 60c+ under Prime95.
If the 440 comes with an HSF that is anything like the 710, I imagine You should be able to at least do 10% OC safely. From what I have gleaned, the lack of L3 cache on the Athlon IIs may be allowing them to run cooler when directly compared to Phenoms of the same ilk. You might be able to get even more than 10% overclock.
-Make sure your case is well ventilated with balanced push-pull fan pressures (though I personally prefer slightly higher intake pressure than exhaust pressure), and monitor your temps obsessively while overclocking.
-Buy a tube of a good thermal paste (AS5 or MX-2 for example usually run for about $10, and contain enough TIM for several applications) if you are using the TIM that was supplied with the stock cooler, and reseat your HSF. If you haven't done this before, do some research, it isn't tough, and very low risk if you take the right static electricity precautions. This step alone can drop your temps significantly.
You may even be able to see 3.5ghz safely on the stock HSF if you have everything set up right, but not having personal experience with that specific CPU, I can't speak from direct experience. Let us know how it goes!