Just picked up a refurb mid-2011 iMac and looking to pick up a new external hard drive to store video and picture files. If I was buying one of the new iMacs that are coming out, I would buy a USB 3.0 drive but the older iMac only has USB 2.0. My question is: should I spend the extra $ and pick up a Thunderbolt drive for the faster speeds or will a USB 2.0 drive be good enough? I plan on storing all our home video files on the external hard drive and will be using iMovie a lot to edit and create projects. Will I notice better performance using iMovie with a Thunderbolt drive for my video content or will USB 2.0 be fine? Thanks.