With the current rise in difficulty, I predict anything below 3TH/s isn't going to make any acceptable ROI period. Like takagari said, you need to get in early when things are dirt cheap. That's incredibly difficult though with all the scams and mouth breathing chip producers out there that can't live up to their production dates and have no comprehension of customer service. There's no way I'm investing in Black Arrow either until they prove they can live up to their estimates. So far, I'm not impressed with how well they keep customers updated, let alone their website (batch 2 is out, but they're still accepting batch 1 orders?). I find it incredibly hard to believe every single staff member they have is busy in chip development and is completely incapable of giving useful update information to customers.