Are you really listing one for sale? There's lots of philosophical questions on this board in regard to prices. :-P
2-3 months projected returns per bitclockers would be reasonable to me. $7.5k -> $13k US sounds fair. I'm a business guy new to bitcoins, but I see a bunch of new, better, systems on the horizon making overpaying for something like this seem a really bad idea. We've all got preorders waiting out there for gear as good or better than this for less, so it's value is going to drop a lot as they catch up with the backlog.
List that sucker under auctions and we'll tell you how much it's worth by the time it's over.
- puffy
