Q: im going to use my computer for video editing , gaming, music, and watching videos
A: It depends on what you're doing. If you're gaming, a good dual core will be better than a quad because games don't take advantage of four cores. But in normal multitasking a quad will be faster. As for a noticeable difference in speed, it really depends on what processors you are comparing in particular. Either way, I recommend you go quad because it's a bit more future proof as more and more applications will be able to take advantage of four cores. And for now it will be plenty fast enough too.