Men jeg kan ikke se mange muligheder i den efter den har fået quad Sli, kan den overhovedet køre det?

1200 Watt hvis med GTX 590, 1000 Watt hvis GTX 580 Men man er jo nød til at være sikker på hvilke kræfter man har at gøre med

Two GTX580's in SLI beat the GTX590 for performance. But when you use SLI or CrossfireX you run the risk of micro-stuttering.
It's nearly always better to go with a single card graphics solution than it is to use SLI, simply for the reason that if you decide you need a graphics upgrade in the future and your motherboard and power supply supports it, then you can simply add another card from the same series and get a big performance boost for not much money.
If you go SLI off the bat and you decide that you want a graphics upgrade in the future then you'll need to buy two more cards, better ones. And that will be far more expensive.

If you decide you want to SLI two GTX580's then you'll need a 1000W power supply or better.

You won't find a game that cannot be maxed out by a GTX580. The 590 is more powerful but it's overkill, especially if you're only running one screen.