with your 2500Mhash/s, you should be doing about 2100 shares per hour, or at 1.3kW 1625 shares per kWh. that's 4.16 or $5.85. still not too great. 19kWh per btc is probably not the most efficient mining setup. did you increase the voltage on your 5830s? if yes, that's probably not efficient (in my case it's not), undo it. go with whatever clocks your stock voltage allows.
I think you did a little too much theorycrafting. If you mine at a pool, just check how much BTC you produced over the last 24h. Those are the real numbers, including pool downtime etc. deepbit shows that directly at the account page. If you calculate with requirered shares, that does not include difficulty increases.
I was just going by the lastest numbers deepbit provides, which varies between 1.3 and 1.5 BTC/day. The MH/s rate deepbit shows me (actual number for a solved block) varies between 2100 and 2300 since overclocking is not quite complete yet. Btw I did not change anything on the voltages.
Shares look different though, I took some of the numbers from deepbit and divided it with the time it took to solve the block, result is 32-33 shares per minute, which is 1900-2000 shares per hour.
You left out all other parts of your system except gpus so you can't really compare to my rigs. CPUs are 50W each, HDDs 15W each, Mainboard itself 10W each, RAM 2x15W each = 105W per rig.
I've disable all I could like second lan, sound, firewire etc. and I don't know what else I could do, besides probably underclocking/volting the CPU which I will do soon.
of course i didn't include difficulty increases. i didn't include variance, either. on btcmine i get about 0.5% stales and have had 0 downtime for the past few weeks.
i can't include difficulty increases because i don't know where the network is going - it can go anywhere:
if i included variance, i'd have to draw a gaussian curve. i don't think the op wanted to know at which % we pay which amount of $ but instead the expectation value.
i have included the 0.5% stale rate.
somewhere around this forums there is a post which says 1 share per minute requires 71 Mhash/s. that's a fixed value as a share is a solved block with difficulty = 1. maybe this explains something (i don't quite understand some of your post). it's much easier to calculate with that, because the chance to find a block is always 1 share divided by difficulty.
