Seems we all have similar figures. ultimately it all depends on how much you pay for power and what your cooling requirements are.
BTW unrelated to the subject, just to clear up things: hashing speed is usually denoted in (kilo)hashes per second = kH/s, power consumption is denoted in Watts = W = J/s since, so hashing speed per W = (kH/s) / (J/s) = kH / J. That kH/J unit has a meaning of how many (kilo) hashes you get per unit of energy you spend. Energy is what you ultimately pay for, although usually you don't see how many J you've spend on your utility bill, instead they quote you kWh = 3600 kJ.
This clarification also let's you calculate your profitability threshold, that is if your 7950 hashes at 4 MH/s, and the average difficulty is about 3000 and the average block reward is 3 Dash/block, you will need on average 3000 * 2^32 Hashes to produce one block which will yield about 3 Dash and it will take on average 38 days to get a block with your hashing speed. So on average you will get 0.08 Dash/day.
Assuming your electricity rate is 0.1 $/kWh and Btc exchange rate is 240 and Btc/Dash rate is 0.011, your card will spend 24 * 0.2 kWh / day * 0.1 $/kWh / (240 Btc/$) / (0.011 BTC/Dash) = 0.18 Dash/day.
You can see you're way below the waterline (you get 0.08 Dash by spending 0.18 Dash) unless:
- Exchange rate goes up
- Difficulty goes down (this will help dramatically as with lower diff now only you need to spend less energy to solve a block but you will also get more Dashes per block)
- Your card uses less power - undervolting
- Your electricity rate goes way down.
If you're speculating that ultimately you'll be profitable because exchange rate will go up then you'd be better off by buying Dash of the exchange directly.
Hope this helps...
