Quote from: bgibso01 on January 21, 2015, 12:55:09 AM

Quote from: mdude77 on January 21, 2015, 12:50:54 AM

Quote from: bgibso01 on January 21, 2015, 12:48:41 AM

So besides noise & heat, does it really pay to underclock vs. stock on the SP20? I tried to run the numbers allowing a total of 4200 watts at the units (not wall). I used 700w for underclock at 1200gh/s and 1200w for 1600gh/s. My calc shows about $697 higher price for 6 underclocked units vs. 4 stock units. The underclocked higher hashrate would take over 600 days to return the higher price of underclocking.

Am I missing something?

Depends on your electricity price. At current BTC/USD value, I'm losing money running at stock.

That's why I used a fixed wattage so that the electric would be the same in the comparison. It's just additional hashrate at lower w/gh but higher $/gh.

You are not missing anything. mdude77 is correct in that it depends on your local electricity price. But it also depends on whether you are planning to buy units or already have them.

If you already have the units, then your goal might be to maximize net income. See https://bitcointalk.org/index.php?topic=521520.msg10146041#msg10146041 for an example. The higher your electricity rate, the more it makes sense to underclock existing units. Your net hashrate will decrease due to the underclock, but your electricity usage will decrease even more with the result that your net profit (income minus expense) actually increases.

In your example you have used a fixed power budget (4200W) and have taken into account the purchase of either 6 underclocked versus 4 stock units. That is a different calculation and, in this case, you are correct in that buying 6 units only to underclock them may not make sense in terms of return on investment. i.e. buying 4 units and running them at stock speeds may recover your initial investment cost sooner than buying 6. But even here it depends on your electricity costs; if your costs are high enough it is possible that stock units will run at a loss (i.e. you will never recover the purchase price), while underclocked units will run at a profit ... meaning that buying 6 underclocked units make more sense than buying 4 stock units.

Or, as the artificial intelligence WOPR concludes in the the 1983 movie WarGames, sometimes "the only winning move is not to play."