ATI 5770 crossfire or 5850

5770 crossfire has better performance however you will not have an upgrade path as you allready have two cards, unlike a single 5850.

...and you can overclock a 5850 to almost 5870 performance with very little effort. And that single card will do better in non-CF friendly games...

...and you can expand in the future...

5850 in US: 299-370. 5870 in US: 420+, 5770 - $150-160. I personally went with 2x 5770 and am now running clocked over a single 5870. That being said if you are not the type to constantly upgrade, 2x 5770 should do you fine till the 6000 series.

im gonna go with the 5850, so i can upgrade, and i have found an xfx xxx edition 5850 for a good price.
Thanks for advice

good decision.
purely on performance, 5770's CF would perform slightly better, but no upgrade path.

Have fun.