I have an i7 and it does well. It's still pretty rough on the processor, but I don't think you're going to find anything that an edit such video smoothly with the current generation processors. At least not using Premiere Pro (what I use)
Actually, before building this computer, I explored some other HD editing programs and found some of them would play the video smoothly (when going along the timeline) on my old Athlon X2 4200. So the software can really make a difference.