joolzg: I live in .se too. With my 7970 I make at least twice as much as electricity costs. That's not unimportant but my driving force is the anarchist part of it, and a currency that will work even when the world economies go down the drain (yeah I'm a pessimist). Call it an investment or insurance.
I must admit the heat is becoming a serious issue tho. Not to mention the noise. But as long as I get more back than I put in I'll keep going.
I use Sapphire 7870 XT's with a fan on them you can get their GPU to 1200 which is 525mh/s the card cost maybe $15 more than a normal 7870 but comes with 2 pcie 6pin cables and a few adapters. it uses around 175watts much less than a 7970.
The Sapphire 7870XT has a lower end 7970 gpu on it. I have them in 5 desktops with stock 375watt power supplies. It just seemed more cost effective with these cards, using less power, not requiring power supply upgrades etc