Hmm not sure if the video editing would benefit from the quad over the dual considering the supporting hardware.... It probably won't matter but I'm not 100% sure. Considering you don't game or do anything incredibly intensive, and you aren't upgrading anything else, I'd say get an E8400 E0 and spend a few bucks on a good CPU heatsink since that component will have to be installed as well. Or if you feel you need the quad, get a 6600 and a heatsink.
Either way, ditch the stock HS. IMO of course.