The last batch if 10 S15's that we acquired was during that little blip when Bitmain was selling them for $1050. Between that and the coupons we had, it paid for the tariff and shipping. The M10 looks like a good machine but @ 65w/TH the efficiency is too low. We're planning to deploy a total of 36 S15 by the end if Jan and run them full power the rest of the winter. That will give us 1PH. Then change them over to LPM starting in May when we start to have cooling challenges. Our mining room should be able to keep up with the heat very well with 36 machines running 850w ea + the Mini's, and we will be mining at a more efficient ratio during the May-Oct when our PoCo increases our electric rates slightly. In order for us to keep our contract rate with the PoCo we have to draw at least 60KVa 24/7, and in July I want to renew that contract for one more year. We subsidize the electric cost for the mining operation so this will make that more manageable and I'm hoping this last equipment upgrade will keep us mining until the halving. Can't really see beyond that, but I don't think there will be anymore new form factors or revolutionary new increases in efficiency in the next 18 months, so this is what we came up with to keep us mining for one more generation of gear. We can support up to 80 S15's on the current rack (we have total capacity of 150KVa), and our power cost goes down the more we use, so if the gear gets cheaper later in the year we can add more capacity if conditions look favorable. We've been mining since the S5's, so this will be the fourth cycle of gear we've gone through.