Actually, even for 4 BTC, it can't ROI. For next 10 days it will make you about 0.08 BTC per day, and if everything goes like before 0.05 the 10 days after that. If you do the calculation and substract the power it uses, it will never pay for self.
Regardless if you calculate the power or not it will never pay for itself with the way the difficulty is going up!