SLI 560 TI Vs. GTX 580 vs Radeon 7970

well if you can't get a 680 which i assume you can't since it's not in your list then go get a 7970 single

I 2nd Tavo_Nova's remark.

SLI/Crossfire is not worth doing, in my opinion.

I would get the single biggest card you can get instead.

The 680s and 7970s are pretty close to equal, the 580s/6970s are from an older generation where the new generation isn't just slapping a new name on the older cards.

Between the ATI 5000s and 6000s and the Nvidia 400s and 500s there isn't much difference. Between the 6000s and 7000s or the 500s and 600s there is a lot more difference.

I would stick with a newer generation card if possible for that reason.

Thus, my suggestion would be the 7970.

If you can get the 680 do so. It is cheaper and faster than the 7970. If you can't get the 7970

SLI or crossfire on card is awesome, gives nice fps on single monitor even those fps are wasted, but well let's go back to reality. having more than 1 card on a single monitor is not good. even if your using 2 lower tier compared to buying 1 better card(unless your adding a 2nd card). as you will be having multiple head ache but can give great eye candy.

I my self would go with sli/crossfire since I use multi monitor and looks awesome, but well also another down side is, your electric bill "might" burn out your bank

gtx 560ti SLi is going to perform similar to a 680.but i would suggest 680.it's a newer card.it has the following pros over 560ti Sli-
great performance even at stock speeds.
no micro-stuttering and compatibility issue.
less heat and noise.
more overclocking.
560ti Sli cons-
compatibility issues in many games.
lotta heat and noise(in comparison to a single 680).
no upgrade in future.
micro-stuttering and driver issues.

i guess you got my point and i convinced you.

Even though 560ti SLI is cheaper in price/frame, it will run hotter, use a lot more power, and generate more heat.

The SLI setup is worse in every way except one, and often it isn't even better in that one way. That should be enough to pretty much rule it out.