In some benchmarks, it appears the 965 actually loses some performance overclocked. Not a lot of headroom, in my opinion.
Your best bet? If seriously interested in overclocking, get a Ph II X4 940 BE (for $190) and overclock to 3.4 Ghz. You can do this on stock cooling and without raising voltages, just a multiplier adjustment. Then you can decide if you're apt to look into oc'ing more.
Ultimately even a slight overclock could possibly reduce processor life. Enthusiasts oc their processors because they can, and because they change them every year. Sometimes even more often.