So after running 26 hour at stock frequency, I have averaged 8600Gh. The projected daily income at Nicehash is showing at $5.88.
This thing does not generate much heat at all. I have it in my office and whereas other heaters generated an intolerable amount of heat such that I eventually removed them from my office to another location, this one can stay. And as I said earlier, noise level is great, I can still hear the wife yell at me from the other room, which isn't always a good thing...
Let's evaluate the Cost per TH/s and furthermore the Net 12 month Profit:
R4 $1385 / 8.6TH/s = $161.05
S9B13 $1600 / 12.93TH/s = $123.74
S9B12 $1442 / 11.85TH/s = $121.67
Your calculation comes up with $5.88 for the 8.6TH/s = $0.68 profit per TH/s
Using this as the basis (I think that this is a little low, but you should use kano.is for best profitability)
R4 $0.68 per TH/s x 8.6TH/s = $5.88 profit per day x 30 days per month = $176.40 profit per month = $1385 / $176.40 = 7.85 months ROI
S9B13 $0.68 per TH/s x 12.93TH/s = $8.79 profit per day x 30 days per month = $263.70 profit per month = $1600 / $263.70 = 6.07 months ROI
S9B12 $0.68 per TH/s x 11.85TH/s = $8.06 profit per day x 30 days per month = $241.80 profit per month = $1442 / $241.80 = 5.96 months ROI
It may look like S9B12 would be the best buy, but look at the long term profitability (12 months).
R4 $176.40 x 12 = $2116.80 profit per year - (2116.80/12) x 7.85 = $1384.74 cost to ROI. $2116.80 - $1384.74 = $732.06 Net 12 month Profit
S9B13 $263.70 x 12 = $3164.40 profit per year - (3164.40/12) x 6.07 = $1600.66 cost to ROI. $3164.40 - $1600.66 = $1563.74 Net 12 month Profit
S9B12 $241.80 x 12 = $2901.60 profit per year - (2901.60/12) x 5.96 = $1441.13 cost to ROI. $2901.60 - $1441.13 = $1460.47 Net 12 month Profit
SUMMARY:R4 $732.06 Net 12 month Profit
S9B13 $1563.74 Net 12 month Profit
S9B12 $1460.47 Net 12 month Profit
S9B13 is the best buy