Ok,

I dont find a spreedsheat about the 7790 and im not sure about how fast this card is.
This card is at 130euros so that not an bad idea.
Have 1gb to 2gb card ram any effect on minig?
 
About the other cards the 58XX series are only 5 on ebay and that are mostly uses or with no guarantee and i dont want to take the risk of destroying a card after the first few month and get no new one >.<
The 6950 are at 300euros i dont know why but it is... pretty crazy.

Next parts maybe
AMD Sempron 145(45w)
Mainboard really dont know im never every have an amd/ati pc >.<
Ram i must go to check this but i think i have 4gb ddr3.
Power i think im going with corsair.
And an normal hdd.

So with 2 7790 and the other hardware the pc run at 250w~ and roughly can this be true?