This is a repost from the AMD forum; it's more appropriate here. I use eyefinity/crossfire with 3 portrait monitors. I get pretty bad screen tearing because vsync doesn't work. As far as I can tell, there is no way to get eyefinity to work with vsync. Searching shows a few cases of this with no solution, although I haven't found solid information, Ie an article from AMD explaining that there are technical issues preventing vsync from working with eyefinity.
If you have vsync working in fullscreen eyefinity, please post here. If you're on an Nvida surround setup, posting whether vsync works or doesn't would be appreciated. I've heard from one person that it works properly on nvidia.