The question isn't really concern with any math calculation ,is just mean you get good return if bitfurry made its promised, or you get nothing...
This is a gamble on pre-order , If I willing to take the risk I will rather go for pre-order by myself ,since more hashrate efficiency than buying this mining contract.
Totally fair sentiment. Though I have a lot of issues with BFL, I do think they will deliver *eventually*. I don't know enough about bitfury to make the judgement though (which is its own concern). I think we will know a lot more about that within the next two weeks. Perhaps that is the time for some to reevaluate this investment.