Always a tough choice. A large facilty or 2, or a new chip comes out that is better and you could easily not ROI. On the other hand, perhaps no new advances happen, and these machines run for months with profitability. I don't think there is a great chance for ROI if you have extra taxes, or high power cost.  If you get the machine in a timely manor, at cost, with low power bills, your chances go up greatly.