if it's anything like the e8400 (3ghz stock c2d) not terrible. i've put one in my mom's kitchen computer with an ssd and 8gb of ram and she hasn't complained yet. idk if it would play games from today, but probably could play portal with a middling gpu. she mainly uses it for keeping 30 chrome tabs open and 3-4 MS word or excell docs open for days at a time, and it's still pretty snappy.
also, if you're going to overclock something, you might as well pick up a used e8400. i was able to find some for less than $10, so basically impulse purchase territory....