I'd still pass on the demo even if it was broken in properly. They're going to tell you what you want to hear. I was looking at a 997 4S (only one on the lot at the time) and it was a "demo" with 4.1 on the clock. The salesman literally told me "Don't worry about it being a demo car, it was just driven by the owners wife on the weekends"
Just me I'd still pass on it, its only 3k difference between that versus new. It'll also proly be one of the last chances to get at a new E9x. If you do order one though I'd really recommend MR over MW. Mineral White is a nice color but MR