Before I replace my Express with an Extreme: 1) How can I tell by looking at the box if I'm looking at the newer dual-band version or the older one? I want to make sure I'm getting the new one. 2) This one seems to keep changing. Can you Time Machine to an AirPort Disk? 3) I'm mainly changing my AirPort Express for an Extreme because I want to Time Machine wirelessly, what other advantages would I have by upgrading? 4) Are people connected to my guest network able to see my AirPort Disk? Thanks!