Please make sure you have adequate cooling as CountMike suggests. Do you have an aftermarket CPU cooler? If not, you shouldn't even consider anything above a very mild overclock.
I used to have a x4 955, and overclocking it was helpful to get another year or so out of the CPU. I used a Xigmatec cooler that was similar to the Hyper 212. You can get a cheap Hyper 212, and that will do a good job.
Check out guides at Overclock.net or here in the Tom's forums before proceeding. http://www.overclock.net/t/525113/phenom-ii-overclocking-guide
The 965 is getting a little old so you are not going to see massive performance increases, but an OC will help a bit.
If you don't want to mess with changing the cooler, which is a pain in the ass, you may just want to OC your graphics card a bit to squeeze out a few more frames.