AntMiner S2 1TH/s Miner (1w/GH/s) Batch 2
Price:      3599 USD ( 8.065 BTC )

AntMiner S1  180GH/s
AntMiner S1 - 0.893BTC

1000/180=  5.56
AntMiner S2 = 6 AntMiner S1
8.065 BTC > 6 x 0.893BTC

8.065 BTC >  5.36 BTC

so buy AntMiner S2 or 6 AntMiner S1 ?
will be ROI if buy AntMiner S2 or 6 AntMiner S1?