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But how do we compare an operating cost with one-time cost? Trying to figure in lifetime costs creates confusion because we don't know what the devices lifetime is: we don't know how long it will last, how long until 13nm ASICs, when really clever SHA256 optimizations make it obsolete, or what its resale value would be. So instead lets use the opportunity cost. Opportunity cost is especially useful when the good in question is durable and can be resold later at a stable price, which may not apply here but it frees us from having to pick a bunch of debatable parameters.
Lets say you have $1000. You could buy a miner or you could put it in another investment, so one way to look at the price of a miner is the forgone income which you could have received by doing something else with it. 8%/yr is a common used figure for very long term average stock market returns, so lets use that.
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You can sell those stocks at any time, and your calculations make the assumption that you will be able to sell the miner again at the same price as you bought it for at any time. I don't think that is a realistic assumption. If you must write it off over e.g. three years, linearly for simplicity, you can add 27.78 USD to the monthly operating costs for a $1000 miner. I have re-done your calculations below assuming three years useful life:
For the BFL:
$1300 costs you $8.36/month in forgone investment income and $36.11/month in lost resale value. At 60 watts it takes 43.83 KWH/month, or $5.26 at .12/KWH to power. Only 11% of the monthly cost ($49.73) is power.
For the BTCFPGA:
$1070 costs you $6.88/month in forgone investment income and $29.72/month in lost resale value. For the BTCFPGA device to match the BFL operating cost ($ * 9/10 =36.60) under this model it must use less than 49.73 - 36.60 = $13.13 in power or 149.77 watts.
Due to lower initial investment per Ghash, the BTCFPGA is still the most profitable at more than twice the power consumption, assuming a three year useful life for both devices. (Power consumption becomes more important with increasing expected lifetime, but one should not forget Moore's Law.)