Some more info. My 2nd 580 finally arrived and with these new cards, you can leave SLI enabled with any performance hits.

Currently I'm running everything maxed on Ultra except no AA and have all 5 instances set to run 60FPS FG and BG. I typically see 60FPS everywhere except zones with loads of people, then it will drop down to 30-40.

I tried with higher AA, and with 4xAA enabled on my main, most of the time, I would see a solid 60FPS, but when changing into new zones, my FPS would drop to 15-20. I'm guessing this has to do with the amount of memory on these cards, as after I active swapped between all windows, the frames will jump back up.

For 5 boxing, these new fermi cards will eat just about everything you can throw at them.