What does history say about where I might be able to pick up a used 27" 2011 iMac (3.1 or 3.4, 1tTB, 4gb) once the new iMacs go on sale? Thinking eBay. Ideally in the first year of ownership is I can buy AppleCare. Will recent buyers let go of their iMacs to get the new shiny thing? Or should I grab a refurb while they're still in supply at apple.com?