Off the top of my head I'm pretty sure that the max safe operating temperature of the Phenom II chips is 65C. So you're under the max but only just. If it were me I'd be wanting to get those temps down a bit more just to be on the safe side.
An aftermarket cooler would be a good investment, although you also have to consider the general airflow through your case as well.
Have a nose through my guide on Overheating and Temperature Issues (link in my sig). It's a pretty complete guide to the most common causes of overheating and what you can do about them. Good luck!