I have a 20TH Bitcoin contract and a 100MH Ethereum contract. I'm only on my 3rd week with Genesis-Mining, but I would say about 5 months on your return is accurate and it mainly depends on how well the coin you are mining is doing in the market. If Eth were to blow up to about $500/coin I would make my money back in less than 4 months.
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RE: Questions on Genesis mining and Mining Rigs