Its seeming that quite a few games that came out this year are starting to put my 560 Tis into quite the bind, with their inability to keep up at high to very high settings at
5670 x 1080 resolution.
I was contemplating the following, with wanting to get the most power per dollars in a sense
2x HD 6970
HD 6990
2 x GTX 580
GTX 590.
So far I'm leaning either towards the 6970s or the 580s due to their performance over their single card counterparts. My question is which would perform better at eyefinity/surround resolutions in crossfire or sli (hard to find a lot of reviews/info on this), and what would be a good price to buy them at (new and/or used)

Side question would be what would my 560 Tis in my system tab currently be worth?