The two main factors of your CPU's lifespan are heat and voltage. Generally, the lower these are, the longer it lasts.
As long as your CPU is well within 'specs' at all times (Which is, for that chip, max 1.5v core, max 62c temp. So being <45c idle, <60c load, <1.4v is ideal), you should be good. It's very very rare that OCing will kill the CPU as long as you're careful about it. It should easily last you until your next upgrade.
You have pretty decent cooling performance for stock, but the 955 BE's heatsink/fan assembly is a nice piece of compact copper pipe design. That heatsink/fan would get quite loud though: small fan, high RPM. You seem to be doing okay as is, but if you want to push any farther than a different cooler is definitely recommended.