With the coming dump of massive ASIC hashing power in the next 3-4 months (Cointerra Terraminers, Kncminer Neptunes, etc.), it is going to be very difficult to ROI in a decent timeframe. Cointerra is starting to ship their 1.66Th/s machines and have beaten Kncminer to the punch. Probably won't see any Kncminer Neptunes until end of April or early May. If you have sufficient capital, would probably be wise to spend half just investing in bitcoins (which will probably double in value by year's end) as a hedge against the further increases in mining difficulty.