2 5850 BE Croosfire vs gtx 580

If anyone is selling an XFX 5850 Black edition or knows anyone that is thats in good condition for a decent price. Please let me know.

Depends, what resolution are you running at? When i had a 5850 it worked perfectly for 1080p, but when I upgraded to 1440p i had to upgrade because another 5850 still wouldnt be enough, so i got a 580 and it works perfectly.

I will be using the 2 5850s at 1080p nothing higher.

Still kinda iffy considering how poorly the 5xxx generation scaled in CF compared to later generations of nvidia. I think they actually both perform quite similarly, but if I had to choose I'd get the 580 for several reasons.
1) you won't run into crossfire problem. Some games have to be patched, some games perform poorly with it, some games dont even work.
2) lower energy bill 302W vs 244W.
3) The 5xxx series doesnt really support tessellation, i never really had a problem with this till i started playing batman.

You can find a used 580 with a warranty still around the ONC market place or on ebay for around $300. Thats how much I got mine for used. Then you could probably make around $100 or maybe a little bit more off your 5850 if its a ref design.

i would go with gtx580 it beat 2 hd 5850 is some games.
http://www.anandtech.com/bench/Product/303?vs=305