Hi Hans, crossfirex eyefinity works if you are using two 5870 or two 5850. I had two 5850 in crossfirex eyefinity running hotfix 9.12. The problem is when I got my 5970 and places one of my 5850 to create a tri crossfirex setup, that is when I got the mad stutters. The tri crossfirex works if you are using one monitor but if you use eyefinity it stutters, hopefully AMD will improve the drivers so you can mix any 5000 series in tri or quad with eyefinity. I got eyefinity with physx running on my setup, 5970 with 9800gt, just remember to get the patch that enables it.