Thanks for your reply. I am not sure about those four 5850s being cheaper than two 5970. They seem to be pretty equal, at least here in Germany (used ones of course). Do you mean 120 bucks for the power per month?

Regarding the 7970, I don't understand why you'd say it would not work. Sure, I did use the calculator, but as I would sell my old GTX 580, I would not spend more than $200 extra. IF I calculated them in, the break even would be in about a year. But as I need this card (or any other high-end card) anyways, I would just not calculate it in. That way I would make profit, even though it's not much. Best case 0.5 BTC per day, according to you at least 0.25 BTC per day (using the .28 USD).

Regarding the rig: Let's first see what I actually have to pay per kWh. I'll keep you posted.