That the 1GB Cards have issues w/ Eyefinity more than a single card does.
So I will have to test older drivers or something later on but anybody have any ideas/hints?
What resolution are you gaming at? I didn't see this in your posts though I may have missed it. I think based on you mentioning getting 2-3 FPS with Anti-Aliasing enabled, and that you have 1 GB cards, it is likely a limitation of your video card memory at high resolutions.
Getting 2-3 frames per second seems to be a common symptom of running out of vram. AA can cause this to happen.
My suggestion is to turn OFF anti-aliasing, and then compare 1 card versus the crossfire setup.
I too use crossfire 5870s, and have had similar issues in games at high resolutions when anti-aliasing is enabled.