Re: [ANN] Technobit 40 GH/s HEX16B(Bitfury ) 462.00 EUR now shipping
Given that Terrahash+ units are not far away then the potential lifespan of < 100GH/S units has to be questioned - it may well be as mentioned that the most profitable option is to sell the equipment now whilst it still has value before these big guns hit the pools. But of course that is not much fun 
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.Also, it depends a lot on the efficiency of the devices. The difficulty cannot increase by 30% every jump forever, it will start to slow down and maybe stabilize (like it did some time after GPU mining started). The big question is this: will my devices still make more BTC than I pay for the electricity? If so, then great.
For the short term, 30% jump seems to be a proper bad case scenario.
I am currently saving the BTC for a future large purchase of a 1TH or bigger device (or a lot of smaller devices, if they are more economical (price/GH/s, power/GH/s, delivery time)).