When comparing prices you need to member that time is money and the earlier more expensive S7 have had been hashing at a lower difficulty for longer. Not sure if anyone has done the maths to show who was better off?
I have 2 S7's and a 3rd on the way (Batch 9 purchased 1-6-16 sent today). I track my purchase and profits all in BTC. If I need to buy cables I usually have to pay USD but I will convert it at the time of purchase to add to my spreadsheet. I usually can get PSU's for BTC on newegg although my latest PSU was purchased with USD because newegg didn't have any 1600 gold, only platinum and titanium which I didn't want to spring for. So all of these include an EVGA 1600 G2 and some of them include extra 14awg extension cords. Here is where I am now.
Batch 5 - 3.79860731 BTC still needed to break even - earned 1.66839269 so far <--Hashing on bitminter
Batch 8 - 4.03911787 BTC still needed to break even - earned 1.01088213 so far <--Hashing on KanoCK
Batch 9 - 3.27 BTC to break even (this is the one that shipped today - supposed to arrive Friday but that seems optimistic - probably won't start hashing for me until Monday)
The new one will go on KanoCK also.
Just out of curiosity, do you also track operating expenses in BTC? I am thinking of primarily electricity costs, though space rental, Internet access, and cooling could be present depending on your situation.
No, I run them at work so I don't pay electric. The boss knows and doesn't seem to care but I keep it reasonable in terms of how many devices I have.